"modification of a living thing to allow it to endure in a foreign climate," 1830, noun of action from acclimate. There is or was a tendency to use this word in reference to animals and plants and acclimation of humans.
1792, "habituate (something) to a new climate," from French acclimater, verb formed from à "to" (see ad-) + climat (see climate). Intransitive sense "adapt to a new climate" is from 1861. Related: Acclimated; acclimating. The extended form acclimatize is now more common in the older sense of this word (generally in reference to plants or animals), leaving to this word the intransitive sense, which more often refers to humans.
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.
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Definitions of acclimatization from WordNet
adaptation to a new climate (a new temperature or altitude or environment);