The story
Probably from ond- (of unknown origin) + se(ro)t(onin) r(eceptor) an(tag)on(ist).
Etymology from Wiktionary, CC BY-SA 4.0.
ondansetron
Today it means: A carbazole derivative (trademark Zofran), C₁₈H₁₉N₃O, that is a serotonin receptor antagonist administered by injection and by mouth to relieve nausea and vomiting, especially during cancer therapy. Full definition →