solid
/ˈsɒlɪd/·솔리드·adjective
firm and stable; not liquid or gas
LatinCEFR A2
Root
Latin 'solidus' (whole, firm, dense)
Latin solidus (whole, dense) → Old French solide → English solid (14th c.)
In a word
Latin solidus = 'whole, dense, undivided'. Etymologically the same family as solus (alone) — 'whole, not hollow inside'. The solid family unfolds 'oneness made firm' — solid (firm), solidify (to become firm), solidity (firmness), solidarity (standing as one block), consolidate (to make into one mass). "Solid" is a physics term, yes — but first the Latin picture of a single mass with nothing missing inside.
Examples
Ice is water in solid form.
The bridge has a solid foundation.
They have solid evidence.
Related
solidifysoliditysolidarityconsolidatesolidus