Definition of diarrhoea noun from the Oxford Advanced Learner's Dictionary

diarrhoea

noun (British English) (North American English diarrhea)
ˌdaɪəˈrɪə
 
; ˌdaɪəˈriːə
 
(also informal the runs) [uncountable]
 
an illness in which waste matter is emptied from the bowels much more frequently than normal, and in liquid form
Symptoms include diarrhoea and vomiting.