The word "nadir" has several related meanings:
- In astronomy, it refers to the point on the celestial sphere that is directly opposite to the zenith and vertically downward from the observer—that is, the direction pointing directly below a particular location.
- More generally, it can mean the lowest point of anything, such as the lowest point in a person's spirits, the quality of an activity, or a situation.
- In medicine, "nadir" is used to describe the lowest point of a clinical symptom or a blood cell count during chemotherapy.
- Figuratively, "nadir" denotes a low or worst point, like the nadir of economic conditions or relations.
Etymologically, the word comes from the Arabic "nazir," meaning "opposite to," reflecting its original astronomical sense of being opposite the zenith.
In summary, "nadir" means the lowest point, either literally (downward direction) or figuratively (lowest level of something).