1826, noun of action from acclimate, "by form-assoc. with words like narrate, narration, in which -ate is a vbl. ending: in acclimate it is part of the stem" [OED]. The word is attested earlier in German and French. Coleridge has acclimatement (1823), which also is found earlier in French.
accidentally
accipiter
acclaim
acclamation
acclimate
acclimation
acclimatization
acclimatize
acclivity
accolade
accommodate
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