From Halopedia, the Halo wiki
Nishum is a term in the Sangheili language roughly translated as "intestinal parasite" or "worm". Sangheili warriors use the term as an insult towards humans. This usage originated from a misunderstanding in some of the earliest military encounters between humans and Sangheili during the Human-Covenant War. The Sangheili initially confused the body armor worn by human infantry for the exoskeleton of an arthropod-like creature. However, closer examination of fallen humans revealed them to be comparatively small and vulnerable creatures, much like parasites inside their armored shells, which they saw as an appropriate comparison. Combined with the Sangheili's collective hatred of humanity at the time, the term entered the common lexicon of Sangheili warriors as a derisive term toward humans and endured among them even after the end of the war.
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