'round-necked' originates from English, specifically the words 'round' + 'neck' with the adjectival suffix '-ed', where 'round' meant 'circular' and 'neck' referred to the part of a garment surrounding the neck.

'round' comes from Old English 'rund' (or Old Norse 'rūn(d)') meaning 'circular, round'; 'neck' comes from Old English 'hnecca' (cognate with Old Norse 'hnekr'); the compound form combining them with '-ed' to form an adjective ('round-necked') developed in modern English through compounding of noun + noun + adjectival suffix.

Initially formed simply to describe the shape of a garment's neck ('having a round neck'), and this descriptive meaning has remained essentially the same into modern usage.