Sentence:  ACCLIMATIZATION, the process of <WSD>adaptation</WSD> by which animals and plants are gradually rendered capable of surviving and flourishing in countries remote from their original habitats, or under meteorological conditions different from those which they have usually to endure, and at first injurious to them. 
Meaning of the word marked with <WSD> tags:  The process of change that an organism undergoes to be better suited to its environment.