thwart -
hinder or prevent (the efforts, plans, or desires) of; "What ultimately frustrated every challenger was Ruth's amazing September surge"; "foil your opponent"
forbid,
foreclose,
forestall,
preclude,
prevent command against; "I forbid you to call me late at night"; "Mother vetoed the trip to the chocolate store"; "Dad nixed our plans"
thwart -
A brace, perpendicular to the keel, that helps maintain the beam breadth of a marine vessel against external water pressure and that may serve to support the rail.
thwart -
A seat across a boat on which a rower may sit.