mononucleosis

The presence of an abnormally large number of white blood cells with single nuclei in the bloodstream.

Infectious mononucleosis.

A viral infection marked by extreme fatigue, high fever, and swollen lymph nodes, caused by an unusually high number of monocytes.

an acute disease characterized by fever and swollen lymph nodes and an abnormal increase of mononuclear leucocytes or monocytes in the bloodstream; not highly contagious; some believe it can be transmitted by kissing