'late-night' originates from the combination of 'late' and 'night', where 'late' meant 'after the usual time' and 'night' referred to the period of darkness.

'late' and 'night' have been used in English since Old English, and their combination into 'late-night' became more common in modern English.

Initially, it meant 'occurring after the usual time at night', and this meaning has largely remained the same in modern usage.