'apert' originates from Latin, specifically the past-participle adjective 'apertus', where the root 'aper-' meant 'open'.

'apertus' passed into Old French and Middle English (seen as forms like 'apert' or 'aperte') and eventually survived in Modern English as the rare/archaic adjective 'apert'.

Initially it meant 'opened' or 'uncovered' (the literal past-participle sense), and over time it developed into the adjective meaning 'open, exposed, or manifest', now chiefly literary or archaic.