Acclimatization

Acclimatization or acclimatisation (also called acclimation or acclimatation) is the process in which an individual organism adjusts to a change in its environment (such as a change in altitude, temperature, humidity, photoperiod, or pH), allowing it to maintain performance across a range of environmental conditions. Acclimatization occurs in a short period of time (hours to weeks), and within the organism's lifetime (compared to adaptation, which is a development that takes place over many generations). This may be a discrete occurrence (for example, when mountaineers acclimate to high altitude over hours or days) or may instead represent part of a periodic cycle, such as a mammal shedding heavy winter fur in favor of a lighter summer coat. Organisms can adjust their morphological, behavioral, physical, and/or biochemical traits in response to changes in their environment. While the capacity to acclimate to novel environments has been well documented in thousands of species, researchers still know very little about how and why organisms acclimate the way that they do.

The nouns and (and the corresponding verbs and ) are widely regarded as synonymous, both in general vocabulary and in medical vocabulary. It has sometimes been asserted that they should be differentiated by reserving acclimatization for a wild/natural process (e.g., shedding heavy winter fur with natural seasonal change) and reserving acclimation for changes occurring in response to an artificial or controlled situation, such as changes in temperature imposed in an experiment. This assertion is not widely known or followed (as the foregoing citations of 6 major dictionaries show), so writers who intend it must explicitly state that it applies within their usage (for example, "in the following discussion, X refers strictly to Y") if they expect their intended meaning to be received by their audience. The synonym is less commonly encountered, and fewer dictionaries enter it.

...
Wikipedia