'fault-finder' originates from Modern English as a compound of 'fault' and 'finder'. 'fault' comes from Old French 'faute' (from Medieval Latin 'fallita'), and 'finder' is formed from Old English 'findan' plus the agent suffix '-er'.

'fault' came into Middle English from Old French 'faute' (itself from Latin forms related to 'fallere'); 'find' comes from Old English 'findan' (Middle English 'finden'), and the agent noun 'finder' developed in Middle English. The compound 'fault-finder' was formed in Modern English as a descriptive compound.

Initially, 'fault' referred simply to an error or failing, and 'fault-finder' meant one who finds faults; over time the compound acquired a more pejorative sense of someone who habitually or unfairly criticizes.