I came across the Spanish word 'inerme', which comes from Latin inermis and means unarmed.

Since the Latin word for arm is 'arma' and the preffix 'in' indicates negation, it is clear that the form 'inermis' is just 'in-' + 'arma', so I wonder: why does it get inermis and not inarmis?


2 Answers 2


I believe this is one of many examples of Latin vowel reduction in word-internal syllables. The basic pattern is that short vowels in word-internal syllables were reduced: the resulting vowel in Classical Latin varies depending on the phonological context, and sometimes on the vowel. In inermis, the vowel is in a closed syllable, which is a context where a reduced short -a- typically turned into -e-.

Another example is ineptus from aptus.

Vowel reduction was not an automatic process in Classical Latin, so there are also examples of words that don't change short -a- into -e- upon prefixation, e.g. ĭnămābĭlis.

  • I think it makes a difference whether the syllable is open or closed. Reduction seems to be more common in (but not restricted to) closed syllables.
    – Joonas Ilmavirta
    Commented Aug 28, 2018 at 10:02
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    @JoonasIlmavirta: Vowels in internal open syllables were reduced also (to -i- in most contexts; to -e- before -r-, or sometimes before a mute + r cluster; sometimes to -u- before a labial consonant).
    – Asteroides
    Commented Aug 28, 2018 at 10:17
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    The standard example of my Latin teacher was in + amicus = inimicus. Same thing there.
    – Arthur
    Commented Aug 28, 2018 at 16:15

All credit of this answer goes to sumelic. I just found further support for his hypothesis, of which I was not aware.

This article states:

Bader (1960: 236) remarks that words prefixed by privative in- (< *en- < *n-) and dis- frequently show vowel reduction (cf. Pultrová 2006: 73, 102-103), such as inimīcus 'unfriendly' (vs. amīcus 'friendly') and difficilis 'difficult' (vs. facilis 'easy'). The list of examples is lengthened by inficētus 'boorish' (vs. infacētus; cf. perfacētus 'very clever'); īnsipiēns 'unwise' [P1.+], whose finite forms (*insipiō) are missing in Plautine Latin (cf. insapiēns [Catul.]; persapiēntis 'very wise' [Cic], nesapius 'ignorant' [Petr.+]); inermis 'unarmed' (vs. arma 'weapons'); iners 'inactive' (vs. ars 'art, skill'); dīmidius 'half (< *dis-; vs. mēdius 'central', cf. rare forms like intermedius, permedius, submedius; see Ernout and Meillet 1985: 393); displiceō 'displease' (vs. placeō 'please', cf. complaceō 'take the fancy', perplaceō 'be thoroughly pleasing'); etc. (but cf. illepidus 'lacking grace', inanimus 'lifeless'). These forms commonly possess a negative sense due to their prefixes. The i-vocalism may thus be phonetically strengthened by a certain emphasis, as Pulgram (1975: 108-109) points out, whereby the following elements presumably underwent vowel reduction, and were influenced by the i-vocalism.

References in paragraph:

  • Bader, Fr. (1960): Apophonie et recomposition dans les composés. RPh 86:

  • Ernout, A and A. Meillet (1985): Dictionnaire étymologique de la langue latine: histoire des mots. 4th, rev. and enl. ed. Paris: Librairie C. Klincksieck

  • Pulgram, E. (1975): Latin-Romance Phonology: Prosodies and Metrics. Munich: Wilhelm Fink Verl

  • Pultrová, L. (2006): The Vocalism of Latin Medial Syllables. Prague: Univerzita Karlova v Praze / Nakladatelstvi Karolinum.

Similarly, pages 222-3 of this (old) book state:

Unaccented Latin ă in the posttonic syllable became at first ĕ, except before l and labials, where it became ŏ. This ĕ became, perhaps about the end of the third century B.C., ĭ in syllables not long by position (except when it preceded r), and before ng; while this o became u or the ü-sound, which in most cases passed into ĭ at the close of the Republican period. Thus the compound of ab and cado became accĕdo (so spelt by Ennius), then accĭdo; from in and arma we have the compound inermis; from sub and rapio first *surropio probably, then surrŭpio (Plaut.), then surripio', from ex and frango, effringo (see ch, iii. 18). Final Latin ă probably became ĕ, and might be dropped (see ch. iii. 37).

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    If final ă became ĕ, why didn't that apply to the nominative singular in the first declension? Was there some other counterfeeding process?
    – Draconis
    Commented Aug 28, 2018 at 16:24
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    @Draconis I know nothing of linguistic theory, but isn't this an issue of "compound" words only? Are you asking why not every final ă became ĕ? As in rosĕ? That's a way more dramatic change, imo.
    – luchonacho
    Commented Aug 28, 2018 at 18:08
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    @Draconis, the 1st declension nom. sg. was originally -ā, and shortened for not entirely clear reasons; presumably this shortening postdates non-initial vowel weakening. There are some other examples of final short vowels which "should have" gone to -i but didn't because they were originally long, e.g. male, ego.
    – TKR
    Commented Aug 29, 2018 at 18:22
  • Vowel weakening doesn't only occur in compound words -- for example, caput / capitis is the same phenomenon.
    – TKR
    Commented Aug 29, 2018 at 18:26
  • @sumelic You're right, sorry -- word-final short vowels behave differently from medial ones. Male is, rather, an example of unexpected final vowel quantity (because of iambic shortening).
    – TKR
    Commented Aug 30, 2018 at 0:03

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