Function: noun
Date: 1875
1 : a serious disease that is prevalent in much of tropical Africa, is marked by fever, headache, lethargy, confusion, and sleep disturbances, and is caused by either of two trypanosomes ( Trypanosoma brucei gambiense and T. b. rhodesiense ) transmitted by tsetse flies
2 : any of various viral encephalitides or encephalomyelitides of which lethargy or somnolence is a prominent feature