cheval
Originally the French word for horse it is now American slang for a woman whom one dislikes or considers to be malicious or unpleasant because they have come between a once happy and serious relationship.
Example:
You and your boyfriend are in a serious relationship, and he suddenly breaks up with you. You find out later that a cheval was the reason for your parting.
You and your boyfriend are in a serious relationship, and he suddenly breaks up with you. You find out later that a cheval was the reason for your parting.