'mouth-watering' originates from English, a compound of 'mouth' + 'watering', where 'mouth' derives from Old English 'mūþ' (meaning 'mouth') and 'watering' comes from the verb 'water' + '-ing' (originally meaning 'to cause to produce water/saliva').

'mouth' comes from Old English 'mūþ' and 'water' from Old English 'wæter'; the compound phrase 'mouth-watering' developed in Modern English (recorded from the 19th century) by combining the literal sense 'making the mouth water' into an adjectival phrase meaning 'very appetizing'.

Initially it referred literally to causing the mouth to produce saliva ('to make the mouth water'), and over time it became a conventional adjective meaning 'extremely appetizing' or 'tempting'.