'ground-floor' originates from Middle English, specifically the words 'ground' and 'floor', where 'ground' meant 'the solid surface of the earth' and 'floor' meant 'the bottom surface of a room'.

'ground' and 'floor' were combined in Middle English to form 'ground-floor', referring to the lowest level of a building.

Initially, it meant 'the bottom level of a building', and this meaning has largely remained the same in modern usage.