Harmless means unable to hurt anybody. A harmless snake, harmless fun, he is perfectly harmless.
Of a person it is faint praise: calling somebody harmless says they are no threat and not much else. Harmless fun and a bit of harmless nonsense are the standard phrases for something that looks worse than it is. Note harmless as used in food and medicine labelling, where it means causing no injury at the doses involved; and that harm itself is both a noun and a verb — do no harm, harm nobody.
1adjectiveharmlessUnable to hurt anybody.
“The snake is completely harmless and looks anything but.”
harmless is a quality of safety.
The word is harm plus -less, one of the plainest formations in English. The -less ending comes from Old English leas, meaning free from, which is the same word inside loose — so harmless originally meant loose from harm.
Proto-Germanic
*harmalausaz — without harm; harmless
Old English
*hearmlēas
Middle English
harmles
English, today
harmless
From Middle English harmles, from Old English hearmlēas, from Proto-Germanic harmalausaz (“without harm; harmless”), equivalent to harm + less. Cognate with German harmlos (“harmless”), Danish harmløs (“harlmess”), Swedish harmlös (“harmless”).
Etymology from Wiktionary, CC BY-SA