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The word "nominal" has a number of definitions.

For example, the Free Dictionary gives seven:

nom·i·nal (nm-nl) adj.

  1. a. Of, resembling, relating to, or consisting of a name or names. b. Assigned to or bearing a person's name: nominal shares.
  2. Existing in name only.
  3. Philosophy Of or relating to nominalism.
  4. Insignificantly small; trifling: a nominal sum.
  5. Business a. Of, relating to, or being the amount or face value of a sum of money or a stock certificate, for example, and not the purchasing power or market value. b. Of, relating to, or being the rate of interest or return without adjustment for compounding or inflation.
  6. Grammar Of or relating to a noun or word group that functions as a noun.
  7. Aerospace & Engineering According to plan or design: a nominal flight check. [...]

[Middle English nominalle, of nouns, from Latin nōminālis, of names, from nōmen, nōmin-, name; see nō̆men- in Indo-European roots.]

This consistent with the definitions in OED3 and other sources.

Most of the definitions are clearly from the sense of "names" and "nouns" - and from that idea of something being only in name, but not in reality.

However, the aerospace sense seems quite different. During a recent rocket launch, the announcer repeated phrases like "Height is nominal. Power is nominal." to mean these values were within the acceptable and expected ranges.

The OED references these sources [Hat tip @tchrist]:

6. (See quot. 1970.)

  • 1966 Aviation Week & Space Technology 5 Dec. 30/1
    The mission is to launch the 800-lb. Prime vehicle to effect a nominal re-entry at 400,000 ft. following injection at 26,000 fps.

  • 1970 N. Armstrong et al. First on Moon vi. 124
    An example of misuse is our use of the word ‘nominal’, which most of the English-speaking world interprets as meaning small, minimal-and we usually use it in the sense of being average or normal.

  • 1970 R. Turnill Lang. Space 94
    Nominal, a favourite word, meaning within prescribed limits; anything from ‘perfect’ to acceptable.

  • 1972 Daily Colonist (Victoria, B.C.) 26 July 3/1
    As one engineer said, ‘She is phenomenally nominal’ — nominal being space jargon for operating-as-planned.

I wonder if anyone can explain that derivation. Is it derived from the other senses of nominal? Is it influenced by the word "normal"?

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Wouldn't it come from definition 4? The differences from expected values are insignificantly small. – Martin Smith Jul 13 '14 at 17:52
It was a supposition not an answer. Hence not posting it as such. – Martin Smith Jul 13 '14 at 17:58
It is very likely (but not certainly, thus this being a comment rather than an an answer) and extension of its use in describing parts and so forth. A nominal "6 volt" battery will only provide exactly 6V under certain specific load, temperature and age conditions, a nominal "2 by 4" is 1½ by 3½ inches (more or less) and may never have been 2 by 4 even before dressing, and so on. – bye Jul 13 '14 at 18:17
I think the 1970 entry sums it up quite well - someone in a space programme made up a new usage for the word nominal. – Frank Jul 13 '14 at 18:18
@Frank - Exactly, and I'm saying that that use of nominal was probably extended by familiar usage within the engineering community, which is why it now means "within specs". – bye Jul 13 '14 at 18:58

The aeronautical sense of nominal derives from engineering where the nominal value is the specified dimension and the reference point for tolerances.

The Free Dictionary offers the following definition (from McGraw-Hill Dictionary of Scientific & Technical Terms, 6th edition) for tolerance:

(engineering) A permissible deviation from a specified value, expressed in actual values or more often as a percentage of the nominal value.

Surprisingly, the sense of nominal used in the preceding definition of tolerance is missing from both the Free Dictionary (via AHD4) and OED3. But the requisite definition is found in the Oxford Dictionaries Online:

3 (Of a quantity or dimension) stated or expressed but not necessarily corresponding exactly to the real value: 'EU legislation allowed variation around the nominal weight (that printed on each packet)'

This usage in engineering long predates the space program. The following is from Douglas T. Hamilton's Gages, Gaging, and Inspection(1st edition; 1918; p.30):

It is, therefore, common practice to specify the "limit" -- that is the deviation from the true or nominal size which is permissible. The limit is generally stated by giving the amount that the dimension may be larger or smaller than the nominal size. The diameter of the shaft for example may be given as "one inch plus or minus 0.001 inch..."

A measurement corresponding to the nominal value is "according to plan or design." Similarly, when using bilateral tolerances the nominal value is by definition "within acceptable tolerances." The aeronautical usage is derived from engineering.

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So the idea of a sentence "Height is nominal" is that while the height may not be exactly at [the correct height], it's nominally at [the correct height]? – sumelic Sep 23 '15 at 6:08

I'm not allowed to comment yet, so I'll take a stab at answering.

I would say it derives from definition 4. In the aerospace industry, to say that something is "nominal" is to say it is within accepted parameters. Everything in the aerospace industry has accepted parameters or "tolerances".

Example: "We will accept a tolerance of this measurement between a and b." Is the same as "This measurement is between a and b, so it is nominal." Which then becomes "This measurement is nominal", where the tolerance equaling between a and b, becomes unstated, yet accepted.

By stating that something is nominal you relay the parameters it meets without having to pronounce all those numbers. And pronouncing many numbers can get confusing.

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The question here is: "How and when did definition #4 arise?" – bye Jul 13 '14 at 19:03
OK. Second try. I certainly don't mind corrections. – distantsmoke Jul 13 '14 at 19:56
One of the definitions of "nominal" according to Wikipedia:en.wiktionary.org/wiki/nominal is "normal. "Normal" is derived from the Latin "normalis" (with a bar over the a). According to the online eytomology dictionary etymonline.com/index.php?term=normal – distantsmoke Jul 13 '14 at 19:59
According to the online eytomology dictionary etymonline.com/index.php?term=normal normal (adj.) "typical, common;" 1640s, "standing at a right angle," from Late Latin normalis "in conformity with rule, normal," from Latin normalis "made according to a carpenter's square," from norma "rule, pattern," literally "carpenter's square" (see norm). – distantsmoke Jul 13 '14 at 20:09
Nice answer. It's a shortening of "The difference between this and expected are nominal" to "This is nominal" – Mitch Jul 13 '14 at 20:36

One possibility overlooked in the other answers is that although nominal eventually came to mean literally "within normal tolerances", the usage could have been introduced in the sense of "nominal deviation from expected value"; i.e. there is deviation (as there must be from any expected value when measuring real things), but it is small enough to be a deviation in name only.

This also nicely fits as explanation for the other questionable meaning that doesn't suit the etymology: "insignificantly small".

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Someone else will hopefully provide some historical evidence. I don't have that to offer.

For my thinking, this connotation comes from the distinction between (a) what something is in name, that is, as set forth in a definition or specification and (b) what a given occurrence of that something is in concrete reality.

The "2-by-4" and other examples cited so far fit this. It especially makes sense for contexts, such as standards, where a name or symbol is invented or formally ascribed to a definition that the standards body formulates.

Such a definition sets forth what something is in name, or nominally. For a given occurrence to fit that name the definition must be matched in some way, often within tolerances specified in the definition.

If it fits then it can be called by that name - it is nominally such a thing. This is the case even if according to some other considerations one might normally not think of it as being such a thing.

It may help to think of the expression at least in name or even in name only.

Those Republicans on the far right of the American political spectrum sometimes criticize centrist Republicans as being "RINO"s (rhinos): R epublican I n N ame O nly. From their point of view the centrists are only nominally Republican, that is, according the definition of being enrolled in the party. They do not consider them to be really Republican, that is, Republican in spirit or actual practice.

The point is this: Use of the word nominally in such contexts emphasizes the possibility or actuality of a discrepancy between (a) the meaning of the name as formally or defined or as normally/conventionally understood and (b) the meaning of some individuals or occurrences that are classified under that name.

Some things called a given name do not, in some sense, seem to really correspond to what one thinks of as what that name means. There is some difference -- in some sense the name does not really seem to fit.

(This difference is close to what is meant by the letter of the law versus the spirit of the law. The former is the nominal meaning of the law.)

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This answer doesn't make sense or provide any evidence. "In name only" means that it doesn't match what it's supposed to be. "Nominal" in aerospace means that it does match what it's supposed to be, which is the opposite meaning. – Ben Crowell Jul 13 '14 at 21:06
@Ben: Please reread what I wrote. If a standards body defines round as within certain tolerances, and if something that might normally be considered round is not round according to that definition, that thing is nominally round (according to that definition). Aerospace, science, the military etc. often use formal/artificial/conventional definitions. And the vocabulary sometimes uses nominal to point out that that is what is meant. If the potential difference in meaning is disregarded/unimportant then there is no need to add nominal to the phrase. (But adding it can become habitual.) – Drew Jul 13 '14 at 21:24
This answer is correct, if a little long-winded. The meaning "within acceptable tolerances" can be derived from the idea "by name" quite handily. It means "close enough to call it that". As @Drew has shown by example, "name" and "nominal" can be used to imply both favorable and unfavorable assesements. – DavidC Dec 23 '14 at 16:44

I would say it is most likely that someone whose mother tongue is not English, once said 'nominal' when they meant to say 'normal'. Unfortunately, it stuck.

I work in the Space industry and the use of 'nominal' is very common amongst my non-English colleagues; even in the non-space parts of their lives.

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Hi Nick, and welcome to ELU. Citing a reference to support your position would make this a much better answer. Otherwise this can be seen as just your opinion, and we try to give answers with some kind of authoritative reference. Since you're here, please have a look at the site tour and visit the help center for guidance on how to use this site. – medica Nov 15 '14 at 13:28

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