'baignoire' originates from French, ultimately from Old French elements related to 'bain' (from Latin 'balneum'), where 'balneum' meant 'bath'.

'baignoire' developed in Old French from words for 'bath' (from Latin 'balneum' / 'balneārium') and eventually became the modern French 'baignoire'; it is occasionally borrowed into English with the same form 'baignoire'.

Initially it referred broadly to a place or thing for bathing ('bath'), but over time it narrowed to mean specifically a bathtub (a fixed or freestanding vessel for bathing).