Eggs or young lice that parasitize human hair; also means trivial complaints or overly detailed criticisms.
From Old English 'hnitu,' related to Germanic roots. The word's shift to mean 'petty criticisms' comes from the expression 'picking nits' (removing lice eggs), which is painstaking work.
Picking nits became a metaphor because removing lice eggs is impossibly tedious—so when someone 'picks nits,' they're doing equally pointless work, which makes 'nit-picking' one of English's most vivid insults.
Complete word intelligence in one call. Free tier — 50 lookups/day.