'smooth-beaked' is a compound formed from 'smooth' + 'beaked'. 'smooth' originates from Old English 'smōþ', where Proto-Germanic '*smuþaz' meant 'smooth'. 'beaked' comes from the noun 'beak', which entered English via Old French 'bec' (also attested in Middle English as 'bek'), meaning 'beak'.

'smooth' developed from Old English 'smōþ' into Middle English 'smoth' and modern 'smooth'. 'beak' appears in Middle English as 'bek'/'beche' from Old French 'bec' and eventually combined as a descriptive compound in modern English as 'smooth-beaked'.

Initially the separate elements meant 'smooth' and 'beak' respectively; when combined as 'smooth-beaked' the meaning remained literal: 'having a smooth beak.'