The meaning of THRASH is to beat soundly with or as if with a stick or whip : flog. v. There are ten meanings listed in OED's entry for the noun thrash, two of which are labelled obsolete. b. "Liar!" Sarah screamed, as she thrashed the child. thrash /θræʃ/ v. It can also indicate a severe defeat or outperforming someone in a competition. . THRASH definition: to beat soundly in punishment; flog. Definition of thrash verb in Oxford Advanced Learner's Dictionary.