adaptation

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The act or process of adapting.
• noun The state of being adapted.
• noun Something, such as a device or mechanism, that is changed or changes so as to become suitable to a new or special application or situation.
• noun A composition that has been recast into a new form.
• noun The alteration or adjustment in structure or habits, often occurring through natural selection, by which a species or individual becomes better able to function in its environment.
• noun A structure or habit that results from this process.
• noun Physiology The responsive adjustment of a sense organ, such as the eye, to varying conditions, such as light intensity.
• noun Change in behavior of a person or group in response to new or modified surroundings.

from The Century Dictionary.

• noun Same as immunization.
• noun The act of adapting or adjusting; the state of being adapted or fitted; adjustment to circumstances or relations.
• noun That which is adapted; the result of altering for a different use.
• noun In biology, advantageous variation in animals or plants under changed conditions; the result of adaptability to, and variability under, external conditions; the operation of external influences upon a variable organism, or a character acquired by the organism as the result of such operation.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act or process of adapting, or fitting; or the state of being adapted or fitted; fitness.
• noun The result of adapting; an adapted form.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun uncountable The quality of being adapted; adaption; adjustment.
• noun uncountable Adjustment to extant conditions: as, adjustment of a sense organ to the intensity or quality of stimulation; modification of some thing or its parts that makes it more fit for existence under the conditions of its current environment.
• noun countable Something which has been adapted; variation.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (physiology) the responsive adjustment of a sense organ (as the eye) to varying conditions (as of light)
• noun the process of adapting to something (such as environmental conditions)
• noun a written work (as a novel) that has been recast in a new form