0 something that is important enough to you to prevent you from agreeing to something, buying something, etc.:
If he says he doesn't want to move, then you need to decide if it's a dealbreaker for you.
We'd prefer the valuation points were all similar, but it's not a dealbreaker.
If a partner won't accept your friends or family, that's usually a dealbreaker in a relationship.
I really liked the device, but the dealbreaker for me was that it only worked with a projector.
That might have been a dealbreaker for me.
This isn't necessarily a dealbreaker.