The Oxford Thesaurus An A-Z Dictionary of Synonyms - thwartv.

1) frustrate, impede, check, stymie, baffle, stop, foil, stump, hinder, obstruct, balk, block, oppose, negate, nullify, Colloq short-circuit: They have thwarted all our efforts to become friendly. --n. 2) brace, cross-brace; (rowing-) seat, bench: These canoes are fitted with two thwarts.