'full-volume' is a modern compound formed from the adjective 'full' (Old English) and the noun 'volume' (borrowed into English from Old French and Latin), literally meaning 'full amount/level of volume'.

'volume' originates from Latin 'volumen' (a roll, a roll of writing); it passed into Old French as 'volume' and into Middle English as 'volume', later taking on senses of 'size, amount' and 'sound level'. 'full' comes from Old English 'ful' meaning 'filled' or 'complete'. The compound 'full-volume' is a straightforward modern English formation combining these elements.

Originally, 'volume' meant a roll or scroll; over time it evolved to mean 'amount' or 'size' and later 'loudness' (sound level). 'full-volume' thus came to mean 'at maximum sound level'.