Diarrhea
late Middle English: via late Latin from Greek diarrhoia, from diarrhein ‘flow through’, from dia ‘through’ + rhein ‘to flow’.
wiktionary
From Middle French diarrie (French diarrhée), from Late Latin diarrhoea, from Ancient Greek διάρροια(diárrhoia, “through-flowing”), from διά(diá, “through”) + ῥέω(rhéō, “flow”). Spelling later altered to resemble the word's Latin and Greek roots.
etymonline
diarrhea (n.)
"morbid frequent evacuation of the bowels," late 14c., diaria, from Old French diarrie, from Late Latin diarrhoea, from Greek diarrhoia "diarrhea" (coined by Hippocrates), literally "a flowing through," from diarrhein "to flow through," from dia- "through" (see dia-) + rhein "to flow" (from PIE root *sreu- "to flow"). Respelled 16c. from diarria on Latin model.
