The antonyms for the word "play act" refer to actions that are sincere, genuine, and spontaneous. Such antonyms include behave, act naturally, and perform genuinely. To behave means to conduct oneself in a way that is fitting for a particular situation without pretending or affecting. Acting naturally implies that one is being truthful and not pretending or acting a part. Performing genuinely, on the other hand, suggests that one is presenting something that is real, authentic, and not fake. In essence, the antonyms for "play act" refer to genuine expressions of character, behavior, and performance.