acclimation (n.) Look up acclimation at Dictionary.com
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.