thwart

Thwart comes from Middle English thwerte, from the adjective thwert ("obstinate, perverse"), which traces to Old Norse þvert, the neuter form of þverr, meaning "transverse."

The word began as a description of something lying crosswise, then took on the sense of being contrary or obstinate, before settling into the verb we use today for actively blocking someone's efforts.

It's related to queer, both descending from this same family of words meaning crosswise or askew.