1. A collective noun for a group of ducks. I started eating my bread on the park bench, and a twack of ducks came over looking to be fed.
2. informal A hard, sharp blow, especially with something flat; a thwack. She gave me a twack on the head for saying she looked chubby in her new jeans. Sometimes the old engine just needs a little twack to get running.
3. informal The sound made by such a blow. He slipped on the ice and hit his head on the pavement with a loud twack.
4. slang A twelve-pack (of beer). I'll bring a twack of Bud Light to the barbecue tomorrow. He got caught trying to buy a twack of beer with a fake ID.
n. a twelve pack of beer (cans). (Twelve + pack.) Let’s pick up a couple of twacks for the game.