'deep-toned' originates from English, specifically the words 'deep' and 'tone' (in the past often seen as 'toned'), where 'deep' traces to Old English 'deop' meaning 'deep, profound', and 'tone' ultimately comes from Latin 'tonus' (via Old French/Medieval Latin) where Greek 'tonos' meant 'a stretching' or 'pitch of sound'.

'deep' changed from Old English 'deop' into Middle and Modern English 'deep', while 'tone' developed from Greek 'tonos' → Latin 'tonus' → Old French/Medieval Latin forms and into Middle English 'tone'. The compound adjective 'deep-toned' was formed in Modern English by combining 'deep' + 'toned' to describe sound quality.

Initially, 'deep' referred to spatial or figurative depth and 'tone' to pitch or timbre; over time the compound came to specifically denote a low, rich quality of sound in voices or instruments.