Definitions:

1. In astronomy, is the point directly below an observer, diametrically opposite to the zenith, or highest point directly above. NOUN
   • During the celestial navigation class, the instructor explained that the nadir is the point directly below us on the celestial sphere, opposite the zenith.
2. Often used to emphasize extreme situations of misfortune or failure. NOUN
   • The athlete's career hit a nadir after a series of injuries.
3. Represents the point in the celestial sphere that intersects a line expanding from the observer's position down through the Earth to the other side. NOUN
   • The nadir of the storm was marked by torrential rainfall and high winds.
4. Used to describe the lowest point or moment of despair and failure in someone's life or in a particular situation. NOUN
   • After losing his job and struggling to find a new one for months, he felt he had reached the nadir of his professional career.

Synonyms:

• abuss
• depth
• low-water mark
• the all-time-low
• the lowest level
• the lowest point
• zero