Verb
(idiomatic) To behave in a manner that is straightforward, honest, or sincere.
(idiomatic, performing arts) To perform a role in a manner that is not comedic or exaggerated.
(idiomatic) To avoid criminal behavior.
Synonym: go straight
Most comic writers like to think they could play it straight if only their public would let them. Waugh is able to be grave without difficulty for he has always been comic for serious reasons. He has his own, almost romantic sense of propriety. V. S. Pritchett
If you play it straight it's funny - the best comedy is always played straight down the middle. The adjustment is understanding from the screenplay that a moment is hilarious. Tom Hiddleston
I think a lot of the instincts you have doing comedy are really the same for doing drama, in that it's essentially about listening. The way I approach comedy, is you have to commit to everything as if it's a dramatic role, meaning you play it straight. Will Ferrell