Zenith is the highest point — literally the point of the sky directly overhead. Nadir is the lowest, the point directly beneath you. Both are used figuratively for the peak and the low point of a career, reputation or fortune, and both came into English from Arabic astronomy.
The core difference
Direct opposites, both astronomical in origin.
- zenith — the point directly overhead; figuratively, the peak: the zenith of his career.
- nadir — the point directly below; figuratively, the low point: the nadir of the crisis.
The Arabic origins
Nadir is from Arabic naẓīr, opposite — meaning opposite the zenith. Zenith reached English through a misreading of Arabic samt (path), the m having been mistaken for ni in medieval manuscript copying. So the word is, strictly, the result of a scribal error that stuck.
The astronomical sense
Both are still precise technical terms. The zenith is the point of the celestial sphere directly above an observer, and the nadir directly below — so they are defined by where you are standing rather than being fixed points.
Frequently asked questions
Which one is the low point?
Nadir. Zenith is the highest point.
Where do the words come from?
Both from Arabic astronomy. Nadir means "opposite" — opposite the zenith — and zenith arose from a misreading of the Arabic word for path.
Are they still technical terms?
Yes. In astronomy the zenith is directly above an observer and the nadir directly below, so both depend on where you stand.