specialization has 5 distinct synonyms spread across 3 of its 3 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.
the act of specializing; making something suitable for a special purpose
the special line of work you have adopted as your career
“his specialization is gastroenterology”
(biology) the structural adaptation of some body part for a particular function
“cell differentiation in the developing embryo”
Synonyms, antonyms and the broader and narrower relations for specialization come from Princeton University’s WordNet. Full sources and licences.