v. thrash synonyms, thrash pronunciation, thrash translation, English dictionary definition of thrash. To strike thrash /θræʃ/ v. . It can also indicate a severe defeat or outperforming someone in a competition. To thrash a person or animal means to hit the person or animal hard and repeatedly: If you thrash someone, you hit them several times as a punishment. See Synonyms at beat. "You stole it. thrashed , thrash·ing , thrash·es v. How to use thrash in a sentence.