Pronunciation: (op"ur-tOO-nis'tik, -tyOO-),[key] —adj. 1. adhering to a policy of opportunism; practicing opportunism.
2. Pathol. a. (of a microorganism) causing disease only under certain conditions, as when a person's immune system is impaired.
b. (of a disease or infection) caused by such an organism: Pneumocystis pneumonia is an opportunistic disease that often strikes victims of AIDS.