treat has 13 distinct synonyms spread across 6 of its 10 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.
interact in a certain way
“Do right by her”
provide with a gift or entertainment
“Grandmother always treated us to the circus”
provide with choice or abundant food or drink
“Don't worry about the expensive wine--I'm treating”
engage in negotiations in order to reach an agreement
“they had to treat with the King”
regard or consider in a specific way
“I treated his advances as a joke”
Synonyms, antonyms and the broader and narrower relations for treat come from Princeton University’s WordNet. Full sources and licences.
an occurrence that causes special pleasure or delight