solution has 5 distinct synonyms spread across 2 of its 5 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a homogeneous mixture of two or more substances; frequently (but not necessarily) a liquid solution
“he used a solution of peroxide and water”
Synonyms, antonyms and the broader and narrower relations for solution come from Princeton University’s WordNet. Full sources and licences.
a statement that solves a problem or explains how to solve the problem
“they were trying to find a peaceful solution”
a method for solving a problem
“the easy solution is to look it up in the handbook”
the successful action of solving a problem
“the solution took three hours”