Harmless/ˈhɑːrmləs/ Definition 1 of 2Pro Tip 1/3Deceptive appearances Looks can be deceiving. 'Harmless' often contrasts with how something looks. Despite its sharp teeth, the fish is completely harmless. Pro Tip 2/3Describing fears Use 'harmless' when reassuring someone that their fear is unnecessary. Don't worry, spiders in this area are totally harmless. Pro Tip 3/3Non-threatening context 'Harmless' is often used to describe activities or behavior that won't cause trouble. The kids are just having some harmless fun in the yard.