Thwart means to frustrate or successfully oppose.
Thwart is a verb.
Synonyms: hinder, inhibit, prevent, cross, foil, circumvent, obstruct, frustrate.
Antonyms: abet, help, support, aid, encourage.
Note: Thwart can also be a noun meaning a seat across a boat especially one that is used by a rower.
I tried to finish the project documentation but my attempts were thwarted at every turn.
Mr.Ravi's efforts to thwart my plans inadvertently ended up helping me.