sentimentalise has 3 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.
make (someone or something) sentimental or imbue with sentimental qualities
“Too much poetry sentimentalizes the mind”
look at with sentimentality or turn into an object of sentiment
“Don't sentimentalize the past events”
Synonyms, antonyms and the broader and narrower relations for sentimentalise come from Princeton University’s WordNet. Full sources and licences.
act in a sentimental way or indulge in sentimental thoughts or expression