specialise has 8 distinct synonyms spread across 5 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. Its one recorded opposite is diversify.
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.
devote oneself to a special area of work
“She specializes in honey bees”
be specific about
“Could you please specify your criticism of my paper?”
become more focused on an area of activity or field of study
“She specializes in Near Eastern history”
evolve so as to lead to a new species or develop in a way most suited to the environment
Synonyms, antonyms and the broader and narrower relations for specialise come from Princeton University’s WordNet. Full sources and licences.