harmless UK /ˈhɑːmləs/US /ˈhɑɹmləs/ adjective3 •not able to hurt or damage anyone or anythingThis snake looks nearly the same as its poisonous cousin but is harmless. •Not intended to harm; inoffensive.His humor can be annoying but is harmless. •(no longer used) Unharmed. formsmore harmless · most harmless