'smooth-bodied' originates from English, specifically formed by combining the adjective 'smooth' + the noun 'body' + the adjectival suffix '-ed' to describe possession of the quality of 'smoothness' in the body.

'smooth' comes from Old English 'smōþ' meaning 'smooth, without roughness'; 'body' comes from Old English 'bodi(g)'; the adjectival use with '-ed' to form compounds (e.g. 'smooth-bodied') is a later productive formation in Modern English for descriptive compounds.

Initially the elements meant 'even, without roughness' (for 'smooth') and 'the physical form or trunk' (for 'body'); combined as 'smooth-bodied' the phrase has long been used to describe organisms whose bodies are smooth, a meaning that has remained stable as a descriptive compound.