Biology. Having a form or function suited to a specific situation; exhibiting specialization (specialization, n. 2a).

Biology. Of an organism or characteristic: that has become modified in the course of evolution to suit an ecological niche or biological…

Imperfectly or abnormally adaptive; characterized by maladaptation.

Biology. Hence of an organism: possessing fitness (see fitness, n. additions c). Occasionally of a variation: conferring fitness.