Which word describes something that is extremely disturbing or distressing?

The word that describes something that is extremely disturbing or distressing is "harrowing." This term specifically conveys a sense of deep emotional pain or anxiety that arises from experiences that are profoundly unsettling. When something is described as harrowing, it implies a level of distress that can evoke feelings of horror or anguish, often related to traumatic events or situations that leave a lasting impact on an individual’s psyche.

While "agonizing," "disturbing," and "traumatizing" share some relevance to distressing experiences, they do not carry the same connotation of depth and intensity that "harrowing" does. "Agonizing" typically emphasizes severe suffering or pain, often physical, rather than just emotional distress. "Disturbing" denotes something that is unsettling but does not necessarily imply the depth of trauma that "harrowing" does. "Traumatizing" relates closely to intense emotional distress but often suggests a focus on the aftermath of an event rather than the immediate impact typified by a harrowing experience.

Thus, "harrowing" stands out as the most appropriate descriptor for something that evokes extreme disturbance or distress.