WordNet sense 1 (the process of adapting to something (such as environmental conditions)):

adaptation, adaption

WordNet sense 2 (an amount added or deducted on the basis of qualifying circumstances):

allowance

WordNet sense 3 (making or becoming suitable; adjusting to circumstances):

accommodation, fitting

WordNet sense 4 (the act of adjusting something to match a standard):

readjustment, registration

WordNet sense 5 (the act of making something different (as e.g. the size of a garment)):

alteration, modification