realization has 5 distinct synonyms spread across 6 of its 6 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.
coming to understand something clearly and distinctly
“a growing realization of the risk involved”
making real or giving the appearance of reality
a musical composition that has been completed or enriched by someone other than the composer
a sale in order to obtain money (as a sale of stock or a sale of the estate of a bankrupt person) or the money so obtained
the completion or enrichment of a piece of music left sparsely notated by a composer
something that is made real or concrete
“the victory was the realization of a whole year's work”
Synonyms, antonyms and the broader and narrower relations for realization come from Princeton University’s WordNet. Full sources and licences.