Pronunciation: (ādz),[key] —n.Pathol. a disease of the immune system characterized by increased susceptibility to opportunistic infections, as pneumocystis carinii pneumonia and candidiasis, to certain cancers, as Kaposi's sarcoma, and to neurological disorders: caused by a retrovirus and transmitted chiefly through blood or blood products that enter the body's bloodstream, esp. by sexual contact or contaminated hypodermic needles. Cf. AIDS virus.