'robust-looking' is a modern English compound formed from the adjective 'robust' and the present-participle adjective-forming 'looking' (from the verb 'look').

'robust' originates from Latin, specifically the word 'robustus', which derives from 'robur' meaning 'hard oak' or 'strength'. 'Robust' entered English via scientific and literary Latin/French usage in the 17th century. 'Look' comes from Old English 'lōcian'/'lōc' (related to Germanic roots) and developed into modern English 'look'; the compound 'robust-looking' is a straightforward 20th/21st-century English formation combining an adjective and a participial adjective.

Initially, 'robust' in Latin suggested 'made of oak' or 'having the strength of oak', and over time its meaning broadened to 'strong, hardy, healthy'; combined with 'looking' it now specifically conveys 'appearing strong or healthy'.