crystalise has 12 distinct synonyms spread across 4 of its 4 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.
make free from confusion or ambiguity; make clear
“Could you clarify these remarks?”
cause to form crystals or assume crystalline form
“crystallize minerals”
assume crystalline form; become crystallized
cause to take on a definite and clear shape
“He tried to crystallize his thoughts”
Synonyms, antonyms and the broader and narrower relations for crystalise come from Princeton University’s WordNet. Full sources and licences.