Nadir refers to the lowest or worst point of something. When used in astronomy, nadir describes the point of the celestial sphere that is directly opposite the zenith and vertically downward from the observer.

// Only once the novel’s protagonist reaches her nadir does she arouse the reader’s empathy, and we root for her to climb back to respectability.

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“Sacrament dives right into the nadir of the 2020 health crisis, following a group of nurses who have moved into makeshift housing near a California hospital, to isolate from their families during the height of the case surge.” — James Folta, LitHub.com, 1 July 2025

Nadir is part of the galaxy of scientific words that have come to us from Arabic, a language that has made important contributions to the English lexicon especially in the fields of mathematics, astronomy, medicine, and chemistry. The source of nadir is naḍhīr, meaning “opposite”—the opposite, that is, of the zenith, the highest point of the celestial sphere which is positioned vertically above the observer. (The word zenith itself is a modification of another Arabic word that means “the way over one’s head.”) Though born of the heavens, both words are called upon to refer to earthy things too, especially a significant point or period of time, be it a high point or low one.