1. To tangle or tie something in a knot or knots: The wind knotted my hair up. Don't let the kittens knot up the yarn.
2. To become tangled or tied in a knot or knots: My shoelaces knotted up. If you don't comb your hair, it will knot up.
3. To make something or someone painfully tense, as from illness or grief: Something I ate has knotted up my stomach. The sad scene at the end of the movie knotted me up. I get all knotted up when I think of the terrible accident.
4. To equal an opponent's score in some contest: The home team knotted up the game. The hockey player knotted it up with a last-minute goal. The game was knotted up at 2-2.