Etymology Dictionary

AMMUNITION,  store for defence.  (Lat.)   Used by Bacon, Advice to Sir G. Villiers (R.)   [Formed with F. suffix -tion, but borrowed from late Latin.]—Low Lat. admunitionem, acc. of admunitio defence, fortification.   [The change of adm- to amm- in Latin words is not uncommon, and is the rule in Italian.]—Lat. ad-, to; and munitio, defence.—Lat. munire, to fortify, esp. to defend with a wall; originally spelt moenire, and connected with Lat. moenia, walls fortifications.   ¶ Curtius connects this with Gk. ἀμύνειν, to keep off, and suggests ✔MU, possibly meaning 'to bind;' i. 403.   Otherwise Fick, i. 724. [※]

ERRATA

Probably (F.,—L.), not (L.)   The Low L. admunitio, not in common use, appears to have nothing to do with it.   The E. ammunition appears to be an E. spelling of the old popular F. amunition, given by Littré as an archaic form of F. munition, and possibly due to misunderstanding la munition as l’amunition.   See therefore Munition.