Noah Webster's New International Dictionary of the English Language

1. (v.) To block or prevent; to frustrate; as, to thwart an attempted change; to thwart a rebellion.

2. (a.) Fig.: Perverse; crossgrained.

3. (a.) Thwartly; obliquely; transversely; athwart.

4. (prep.) Across; athwart.

5. (n.) A seat in an open boat reaching from one side to the other, or athwart the boat.

6. (v. t.) To move across or counter to; to cross; as, an arrow thwarts the air.

7. (v. t.) To cross, as a purpose; to oppose; to run counter to; to contravene; hence, to frustrate or defeat.

8. (v. i.) To move or go in an oblique or crosswise manner.

9. (v. i.) Hence, to be in opposition; to clash.