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1.
Two people involved in a romantic or sexual relationship. They aren't blood related, but are so close in kinship or friendship that they might as well be. This could include step-family, family friends, god-siblings, etc.
Person 1: "Andy, just get with Sandy already. What are you waiting for?

Person 2: Ew, man! We've known each other since the first grade. That's like kincest.
by Cicinotouch December 21, 2013