'incompetent' originates from Latin, specifically formed from the prefix 'in-' (meaning 'not') + 'competent' from Latin 'competens' (present participle of 'competere'), where 'competere' meant 'to come together, be suitable'.

'incompetent' entered English via Medieval/early Modern Latin 'incompetens' (and later borrowings through French/Latin), and eventually became the modern English word 'incompetent' in the 16th–17th centuries.

Initially it meant 'not meeting requirements or not suitable'; over time it has come to be used primarily as 'lacking ability or skill' in modern English.