According to Etymonline, ammo has been used as a shortened form of ammunition since 1917. Why does the shortened version end in o instead of u? The only reason I can think of is that it matches other shortened forms like info and photo, but information and photograph actually have an o in them, so I'm not sure that's it. Does anyone have any insight into this?


1 Answer 1


I think it's part of a larger pattern in English in which long words truncated at the second syllable often pick up an -o ending instead of retaining the natural vowel sound and spelling that occurs in that second syllable. Here are some examples:

aggro [aggravation/aggression]

ambo [ambidextrous]

ammo [ammunition]

camo [camouflage]

combo [combination]

convo [conversation]

distro [distribution]

invo [invitation]

limo [limousine]

mono [monaural/monophonic]

provo [provisional]

Valpo [Valparaiso University]

When a phenomenon occurs repeatedly, as this one does, it suggests that the tendency to favor -o endings in truncated words over -a, -au, -e, -i, -ou, and -u endings reflects a genuine, though informal preference in the language, at least for the moment. I don't know whether this particular phenomenon has been discussed in a scholarly setting, but I wouldn't be at all surprised if it has.

  • 1
    1+ Really a good observation.
    – rogermue
    Jun 2, 2015 at 12:20
  • 2
    Excellent, although you might reconsider camouflage. While spelled with an "ou" it is (as far as I know) pronounced just like "camo". This may be a recent development. Jun 2, 2015 at 14:15
  • @WhatRoughBeast I've only ever heard camouflage pronounced with a schwa in the second syllable, whereas camo has a ‘long o’. Jul 7, 2016 at 19:24
  • @JanusBahsJacquet - I think it may be a function of the community. If it is usually referred to as simply "camo" with a long O, on the occasions when the entire word is used the "flage" is tacked on with no change in pronunciation. If the speaker uses the long form commonly, the pronunciation is as you suggest. At least, that's been my experience. Jul 7, 2016 at 20:21

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