'natural-sounding' is a modern English compound formed from the adjective 'natural' and the present participle 'sounding' (from the verb 'sound'). 'natural' originates from Latin, specifically the word 'natura', where 'natura' meant 'birth, innate quality'.

'natural' entered English via Old French/Anglo-Norman 'naturel' from Latin 'natura'; the verb 'sound' (whose present participle gives 'sounding') goes back to Old English roots meaning 'to make a noise' and later broadened. The compound 'natural-sounding' arose in modern English by combining these elements to describe something that 'sounds like the natural thing'.

Originally, 'natural' meant 'of or relating to birth or nature' and 'sound' related to producing noise; over time 'natural' acquired senses of 'normal' or 'genuine', and 'natural-sounding' came to mean 'having the quality of seeming genuine or not artificial'.