pneu·mo·cys·tis 
(n′mə-sĭstĭs, ny-)
(n′mə-sĭstĭs, ny-)n.
Any of a group of fungi of the genus Pneumocystis, especially P. jirovecii, which causes pneumonia in immunocompromised individuals.
[From New Latin Pneumocystis, genus name : PNEUMO- + New Latin cystis, cyst; see CYST.]