Synonyms for Thwart (same or very similar meaning)
WordNet sense 1 (a crosspiece spreading the gunnels of a boat; used as a seat in a rowboat):
cross thwartWordNet sense 2 (hinder or prevent (the efforts, plans, or desires) of):
baffle, bilk, cross, foil, frustrate, scotch, spoilFrom the ODE community, based on WordNetadd/edit