WordNet records no synonym and no antonym for acting out. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
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.
a (usually irritating) impulsive and uncontrollable outburst by a problem child or a neurotic adult
(psychiatry) the display of previously inhibited emotions (often in actions rather than words); considered to be healthy and therapeutic
Synonyms, antonyms and the broader and narrower relations for acting out come from Princeton University’s WordNet. Full sources and licences.