1275-1325;late Middle Englishadmonish, amonesche, admonesse, amoness,Middle Englisha(d)monest (with -t later taken as past participle suffix) < Anglo-French,Old Frenchamonester < Vulgar Latin*admonestāre, apparently derivative of Latinadmonēre to remind, give advice to (source of -est- uncertain), equivalent to ad-ad- + monēre to remind, warn
early 14c., from O.Fr. amonester (12c.), from V.L. admonestare, from L. admonere "advise, remind," from ad- "to" + monere "advise, warn" (see monitor). The -d- was restored on L. model. The ending was infl. by words in -ish (e.g. astonish). Related: Admonitory (1590s).