The colloquial term for a monogamous male who intentionally gets into relationships with females who are in polyamorous relationships. The male gets into these relationships with the goal of removing the female from her other partners and securing her in a monogamous relationship.
A polyamorous male will sometimes become a Cowboy by accident when he falls heavily for a polyamorous female.
The female counterpart for this term is Cowgirl.
Justine warned her polyamorous friend Alexis about Henry, who she’d just met. “Be careful around Henry, I heard that he’s a Cowboy, he’s gonna try and steal you for himself!”