noun.
The physiological adaptation of an animal or plant to changes in climate or environment, such as light, temperature, or altitude.
The Century Dictionary and Cyclopedia
noun.
The act or process of acclimatizing, or state of being acclimatized; the modification of physical constitution which enables a race or an individual to live in health in a foreign climate.
the GNU version of the Collaborative International Dictionary of English
noun.
The act of acclimatizing; the process of inuring to a new climate, or the state of being so inured.