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.