The nadir (frae Arabic: نظير‎ / ALA-LC: naẓīr, meanin "opposite") is the direction pyntin directly ablo a pairticular location; that is, it is ane o twa vertical directions at a specified location, orthogonal tae a horizontal flat surface thare.

Diagram shawin the relationship atween the zenith, the nadir, an different types o horizon. The nadir is opposite the zenith.