'nightclothes' originates from the combination of 'night' and 'clothes', where 'night' refers to the time of darkness and 'clothes' refers to garments worn.

'nightclothes' evolved from the Old English word 'niht' meaning 'night' and 'clāþas' meaning 'clothes', eventually becoming the modern English word 'nightclothes'.

Initially, it meant 'clothes worn at night', and this meaning has largely remained the same in modern usage.