If you mean solid as a state of matter, there are three (the other two are liquid and gas) so there is not one that is exactly an opposite of one ofthe others.
If you are using solid to mean sturdy or well-constructed, one opposite would be flimsy.
solid.
Liquid
Stuipid
Liquid
sturdy, solid
solid
Yes, an antonym is the opposite, and since solid means that it is full on the inside, while hollow means to be empty, so they are the opposite
An non-example of a crystalline solid would be the complete opposite of it, an amorhous solid.
If the type of solid (die) is a Platonic solid, then the opposite sides add to the number of faces plus one. For example, a cube's opposite sides add to seven.
The opposite phase change (solid to liquid) is liquefaction.Where it means to strengthen or coalesce, the opposite could be fragmentation.
The changing of gas into solid is sublimation. it is the opposite of evaporation the changing of solid into gas.
A liquid or solid (not a liquid gas)