Wiktionary
n. (context idiomatic English) An issue which causes a relationship (especially in business) to fail.
Wikipedia
Deal Breaker is a 1995 thriller novel by Harlan Coben and is the first of the novels which feature Myron Bolitar.
Usage examples of "deal breaker".
But that's just extraneous stuff, important, sure, but not a deal breaker.
When the notion had first come up, three months ago, he had argued against including live subjects, to the point at which Colonel Oscar Henderson, the bean counter in charge of funding this project, pushed the issue to the level of a deal breaker.
She's got a great nose for danger, she's not afraid of a decision, she's more of a deal maker than a deal breaker, and she doesn't blush easily.
We are absolutely and unequivocally opposed to such language, and I can tell you right now, Jonathan, that this is a deal breaker for us.