The word hermeticity as (for the lack of better definition, hence the question) “the quality of being hermetic” (not to be confused with mathematical hermiticity, which is also absent from the general dictionaries) seems to be widely used in technical literature. Yet, I am having hard time finding a bona fide definition in any decent dictionary or encyclopædia available on-line. Britannica acknowledges its existence, and via OneLook I only got one reference to the translation from German Hermetizität. OED, Cambridge and M-W turn up nothing.

It could be the case that the use of the suffix -ity to form “nouns denoting quality or condition” is sufficient, but why, for instance, have plasticity if I can get the definition “the quality of being easily shaped or moulded” from the definition of plastic: “(of substances or materials) easily shaped or moulded” (all quotes from OED)? Why not the same treatment of hermeticity?

It can be presumed that such word might appear in unabridged dictionary, but then again, why this term (in all forms, such as hermetic) is not more widely used? From my experience people prefer using the terms water- or air-tight, but hermetic works better both as a general term, and in situations when saying “air-tight liquid hydrogen container” is as semantically wrong as it is technically non-descriptive (it may be air- or water-tight, but not liquid hydrogen-tight).

I think, the usage frequency angle is important in this question. It seems strange to me that this term (again, in all forms) is not widely understood (or used) amongst English-speakers (again, from my limited experience), while, for example, any graduate of a Russian public grade school who took a science class (i.e. any) would understand this borrowed word, even though there are native equivalents for air- and water-tight.

  • When I hear someone use a word like hermeticity I imagine they are Russian, and mistakenly taking a Russian word as English. Or perhaps some other language.
    – GEdgar
    Jan 27, 2013 at 1:57
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    @GEdgar, if you try hard enough, you could also imagine throng of English-speaking scientists and engineers using that word. :)
    – theUg
    Jan 27, 2013 at 2:50
  • Well, "English-speaking" maybe, but Russian nonetheless. And mistaken, too, in my opinion.
    – GEdgar
    Jan 27, 2013 at 14:10
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    @GEdgar why would Russian-speakers be any more likely to use a word derived from a Greek name combined with common English suffixes, than English speakers? I'm surprised to learn the word is the same in Russian.
    – Jon Hanna
    Jan 27, 2013 at 15:34
  • I chose Russian in my comment because I do know some Russian-Americans who use strange words with -icity tacked on.
    – GEdgar
    Jan 27, 2013 at 17:55

3 Answers 3


It's the same reason dictionaries don't usually explicitly list standard plurals, verb inflections, etc.

In the case of plasticity, for example, the base word plastic has multiple "shades" of meaning. Without the definition, you might think perhaps it meant the proportion of plastic incorporated in a composite material. Okay, not likely, but you get my drift.

In the case of hermetic, it doesn't really matter if you don't know which precise meaning is embodied in hermeticity (so far as I'm aware, effectively they all are). Occam's razor and all that.

It's not all that common, and anyone reading it who doesn't recognise the word couldn't fail to discover an entry for hermetic if they check any dictionary. They'll figure it out.

It's also worth copying in this from OED

2 b. hermetic seal, hermetic sealing: air tight closure of a vessel, esp. a glass vessel, by fusion, soldering, or welding; also applied in Surg. to a method of dressing wounds (see quot. 1886).
Also fig. Hence hermetic for ‘hermetically sealed’. [emphasis mine]

That's one of about a dozen definitions for hermetic in the OED entry, and all the rest relate closely to the original literal pertaining to Hermes Trismegistus, and the ... writings ascribed to him.

From which I conclude that standalone adjectival hermetic in OP's sense is probably relatively new, and the extrapolation from this to an abstract noun for quality of being hermetic even newer. Perhaps the dictionaries just haven't caught up yet.

  • His sense is newer than those relating directly to Hermes Trismegistus, but still quite old at well over a century, and probably more common now. It shares the derivation as the tradition that grew out of the pseudepigraphical writings ascribed to him influenced alchemy and the term survived into modern chemistry. The most prominent 19th & 20th C survival of the term in the earlier sense is probably in the name of The Hermetic Order of the Golden Dawn, which is pretty big in terms of Western esoterica, but mostly a footnote in the biographies of Yeats, Æ, et al to people outside that field.
    – Jon Hanna
    Jan 27, 2013 at 1:21
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    @Jon Hanna: Obviously. The one and only OED subsection for this sense, as cut&pasted, mentions 1886 for hermetic = air tight, but that's specifically in combinations such as hermetic seal. I don't know when plain hermetic came to be used for hermetically sealed, but it was probably much more recent. I can see a (possibly misdated) 1922 instance of hermeticity of the seal, but other than that, the earliest is 1931 For ensuring "hermeticity" both on the plug and on the handle-leg... where it's important to note the quote marks suggesting "new and unusual usage". Jan 27, 2013 at 1:44
  • Oh, yes I suppose in the physical sciences "hermetic seal" and "hermetically sealed" were cranberry collocations with the word not used outside of that phrase.
    – Jon Hanna
    Jan 27, 2013 at 1:50
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    Interesting to note that modern technological meaning of this word appears to enter Russian earlier (1870s) than English. I even asked RusL&U question about it, if you would kindly take a look-see.
    – theUg
    Jan 27, 2013 at 18:45
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    @theUg pointing to just when the modern sense arose would be tricky because when alchemy became chemistry, hermetic came with it, but at what point do we call alchemy chemistry? I'd note that hermetically sealed was a buzz word for a while when Otto von Guericke demonstrated his Magdeburg hemispheres in 1656. It matches the modern use, and the news from Germany travelled to both Britain and Russia, so I'd expect it to definitely be found in that sense in both British and Russian, in that year.
    – Jon Hanna
    Jan 28, 2013 at 1:19

Dictionaries document usage. If a specialised word is not well-used, it may not be listed. It may also not be listed if it can be deduced from constituent parts.

As you found, hermetic is listed, and -icity is listed:

-icity, suffix a compound suffix formed by the addition of the [Latin] suffix -tāt- (see -ty suffix1) to adj. stems in -ic. On the analogy of these, abstract nouns in -icity in English are formed freely upon adjs. of any origin in -ic: e.g. apostolicity, atomicity, authenticity, catholicity, domesticity, eccentricity, elasticity, electricity, publicity.

-ty, suffix1 Forming ns. denoting quality or condition

Hermeticity is the quality or condition of being hermetic.

I would guess that more common words are included because they are more likely to crop up and be enquired upon; a rarer word like hermeticity is likely to be used in contexts where readers know of the -icity suffix and the hermetic root and can deduce the meaning.

In the case of the OED, they publish their criteria for inclusion, and my guess is not inconsistent:

The OED requires several independent examples of the word being used, and also evidence that the word has been in use for a reasonable amount of time. The exact time-span and number of examples may vary: for instance, one word may be included on the evidence of only a few examples, spread out over a long period of time, while another may gather momentum very quickly, resulting in a wide range of evidence in a shorter space of time. We also look for the word to reach a level of general currency where it is unselfconsciously used with the expectation of being understood: that is, we look for examples of uses of a word that are not immediately followed by an explanation of its meaning for the benefit of the reader. We have a large range of words under constant review, and as items are assessed for inclusion in the dictionary, words which have not yet accumulated enough evidence are kept on file, so that we can refer back to them if further evidence comes to light.


Frequency is important, particularly with the less full dictionaries. Even with the full OED (the multi-volume print or subscriber-only online)...

... Even the OED does not set out to include every specialized technical term or slang or dialect expression ever used. New words are constantly being invented, developed from existing words, or adopted from other languages. Most will be used rarely, or only by a small group of people. This means that an unlimited number of words may occur in speech and writing which will never be recorded in even the largest dictionary.

Furthermore, what exactly is a word? Clearly we should include single units such as cat and dog. But are the plurals cats and dogs separate words? Should we include compounds such as walking stick, which are made up of two existing words? There are an almost unlimited number of such two-word compounds, which can't all be included in a dictionary. And what about abbreviations like BBC and Dr, or proper names such as London, Nelson, and Harry Potter: are they words? As you can see, the question is not a straightforward one.

With the less complete dictionaries who do not have the same historical aim, but primarily aim to advise as to definition there is an even greater pressure to not include less common words, and less common senses (I note that some which do include hermetic in the sense you are talking about, do not include hermetic in the sense of religious and magical traditions based on writings ascribed to Hermes Trismegistus, or on Hermetic poetry, even though it is through such Hermeticism's influence on alchemy that the term hermetic for a seal such as you use, came about. (Personally, I'd be more familiar with the Hermes Trismegistus-based definition than the scientific, but there are fewer of us writing about Western estoreic traditions than about the physical sciences).

Popularity must be a consideration, if we were to consider the absurd example of a dictionary that did have hermeticity but did not have fish or dog. When we wonder about hermeticity vs plasticity (as you give as a counter example yourself), then we can see the latter much more widely attested:

ngrams comparison of hermeticity and plasticity

Not that hermeticity is absent from that chart; we find it from 1935 on, but compared to plasticity it is very rare indeed.

Similarly, that hermeticity is clearly hermetic (listed in most dictionaries of reasonable size) turned into a noun of -icity form, means that the benefit of including it is further reduced. So between it's rarity and the ability of readers knowledgeable in English to deduce it (and they could even coin it themselves if they didn't know it) makes it a strong candidate for exclusion.

More importantly still, what you deduce from -icity would be correct. In cases where the word has moved into new shades of meaning, or where the senses of the -icity do not match the senses of the -ic form in terms of how current they are, there would be a new pressure toward inclusion rather than exclusion.

There's no hard and fast rule, and Collins does include it, but considering these two factors acting in tandem, I don't find its absence from most as surprising.

Incidentally, this New Yorker article is both relevant and interesting in its own right.

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