Perhaps this is a weird question, but I couldn't find an answer via etymologies.

When something is "impregnable" it means "cannot be broken into."

But, when something is "impregnated", other than the analogous "to make a female with child", it means to "fill" or "saturate", but this almost seems an antonymous verb for "impregnable."

The definition of "impregnable" makes it seem as though the appropriate verb for "impregnate"'s definition should just be " pregnate."

Does anyone know why there is this discrepancy?

I hope I am being clear, thank you.

EDIT: My question has been previously asked here, for all interested. Why does "impregnable" mean *cannot be impregnated*?

  • i believe the prefix "in" has TWO meanings. one is "into"/"towards". the other is "not, opposite". there are any number of examples of the first meaning .. say, infiltrate, immigrate etc etc. ("im" and "in" are just the same, different spellings it seems.) You can find this out by looking up "im-" (or "in-") in a dictionary.
    – Fattie
    Jun 8, 2015 at 6:11
  • I'm not sure I've ever seen an OP flag their own question as a duplicate before. Jun 8, 2015 at 7:03
  • There are other words starting im... or in... which, like impregnate are not negatives, the most obvious one being inflammable. Contrary to what some non-native speakers think, this is not a negative of flammable but indicates that something can easily catch fire.
    – WS2
    Jun 8, 2015 at 7:58

2 Answers 2


They just have different etymologies: prenable vs praegnare

Impregnable (adj.):

  • early 15c., imprenable "impossible to capture," from Middle French imprenable "invulnerable," from assimilated form of in- "not, opposite of" (see in- (1)) + Old French prenable "assailable, vulnerable" (see pregnable).


  • 1600, from Late Latin impraegnatus "pregnant," past participle of impraegnare "to render pregnant," from assimilated form of in- "into, in" (see in- (2)) + praegnare "make pregnant"


  • That's interesting. So the similar appearance of the words in modern English, and the (sort of roughly) opposite meanings is just a coincidence? Jun 8, 2015 at 6:14
  • 1
    As far as I can see, yes!
    – user66974
    Jun 8, 2015 at 6:17
  • huh? Jonathon. the prefix "im" has TWO POSSIBLE MEANINGS. (the two meanings are totally different.) Please note that it is utterly 1000% commonplace in English that words (or prefixes) have more than one meaning.
    – Fattie
    Jun 8, 2015 at 6:18
  • They are not, in any way whatsoever, "roughly opposite". They are utterly unrelated, in any way. If you are seeing "roughly oppositeness" you are being totally confused, perhaps by one specific example. one meaning of "in-" is "non, negation". The other meangin of "in-" relates to "insertion". these two meanings are not even similar in anyway at all they are like "yellow" and "binnacle" - no similarity whatsoever.
    – Fattie
    Jun 8, 2015 at 6:20
  • 1
    I was referring to the words "impregnate" and "impregnable," not the prefix "im." From the etymologies, there is more going on that differing use of than prefix. Jun 8, 2015 at 6:27

Here, the 1 and 2 meanings of "im-" are completely spelled out with examples.


Note that (in both cases) "im-" and "in-" are just two variant spellings of the same thing; there are any number of word examples of all four possibilities.

  • You obviously mean "meanings of im- ," not in- , although they are directly related. There may be better sources of information on this.
    – Kris
    Jun 8, 2015 at 7:24
  • "im-" and "in-" are just two different spellings of the same prefix. look, I'll change it and state that explicitly.
    – Fattie
    Jun 8, 2015 at 7:30
  • 1
    It's not that simple, they are applicable in different cases.
    – Kris
    Jun 8, 2015 at 7:33

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