'nitpicker' originates from English, specifically formed from the word 'nitpick' with the agentive suffix '-er'; 'nitpick' itself comes from 'nit' meaning 'egg of a louse' and 'pick' meaning 'to pick or remove'.

'nitpick' developed in colloquial English in the late 19th to early 20th century as a literal action of picking nits (lice eggs); the agent noun 'nitpicker' arose from adding '-er', and the modern plural form became 'nitpickers'.

Initially, it meant 'to pick nits (lice eggs)' literally; over time it evolved into the figurative meaning 'to find and criticize trivial faults', so 'nitpicker' now commonly means 'a person who does this'.