'curved-legged' is a Modern English compound formed from 'curved' (the past participle/adjective from the verb 'curve') and the adjectival suffix '-legged' (meaning 'having legs of a specified kind').

'curve' ultimately comes from Latin 'curvare' (via Old French and Middle English), where the root 'curv-' meant 'to bend'; 'leg' goes back to Old Norse 'leggr' (and Old English cognates) meaning 'leg'. Those components combined in Modern English to form descriptive compounds such as 'curved-legged'.

Initially the components referred separately to 'bent' ('curved') and 'leg' ('leg'); over time they combined to form the adjectival compound 'curved-legged', whose meaning — 'having bent or curved legs' — is basically literal and has remained stable.