'low-necked' originates from Modern English as a compound of 'low' + 'neck' + the adjectival suffix '-ed'. 'low' ultimately derives from Old English (via Middle English) where forms such as 'hlēow'/'low' conveyed the sense 'not high'; 'neck' comes from Old English 'hnecca' meaning 'neck'; the suffix '-ed' forms adjectives indicating 'having (a specified) neck'.

'low-necked' was formed in Modern English by compounding the words 'low' and 'neck' with the adjectival '-ed'. The elements evolved from Old English 'hlēow' (-> Middle English 'low') and 'hnecca' (-> Middle English 'neck') to become the modern components that produced 'low-necked'.

Initially the components simply meant 'low' and 'neck'; combined as 'low-necked' the phrase has long described garments with a low neckline and continues to carry that same sense today.