'solid' originates from Latin, specifically the word 'solidus', where the root 'solid-' meant 'firm, whole'.

'solidus' passed into Old French as 'solide' and Middle English as 'solid', eventually becoming the modern English word 'solid'.

Initially it meant 'firm, whole' in the sense of solidity or wholeness; over time it came to refer specifically to the physical state of matter that is firm and has definite shape and volume.