'smooth-veined' is a compound formed in Modern English from 'smooth' + 'veined'. 'smooth' originates from Old English 'smōþ' meaning 'having no roughness', and 'vein' originates from Latin 'vena' (via Old French 'veine') meaning 'a blood vessel' which extended to mean a streak or rib in leaves and rock.

'smooth' comes from Old English 'smōþ' and retained the core sense of 'even, without roughness'; 'vein' comes from Latin 'vena' through Old French 'veine' and Middle English, where it came to be used for the ribs or streaks of leaves. The compound 'smooth-veined' is a relatively recent descriptive formation in botanical English, combining those elements to describe leaf venation.

Originally, 'smooth' simply meant 'even or without roughness' and 'vein' primarily meant 'blood vessel' (later extending to streaks or ribs); together they evolved into the specialized botanical sense 'having veins that are smooth or not raised.'