To greatly distress or torment someone emotionally; or as a noun, a farming tool with teeth or spikes used to break up and smooth soil.
From Old Norse 'herja' (to plunder or ravage). The agricultural tool sense comes from its harsh, scraping action; the emotional sense evolved from the violent imagery of something being raked or torn apart.
The same word describes both a farming tool and emotional anguish because the connection is visceral—imagine soil being scraped and torn apart by the harrow's teeth, and you can feel why 'harrowing' became the perfect word for an experience that tears at your emotions.
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