The Nadir, in Latin imum coeli and commonly abbreviated IC, is the point opposite the Midheaven, where the ecliptic crosses the meridian below the horizon, and it is the cusp of the fourth house. Its significations are the foundations of a life: the home, the land, the family and its origins, the father in some schemes, ancestry, and in the classical texts the end of the matter, the outcome or the grave. The word nadir comes through medieval Latin from the Arabic nazir, opposite, and in strict astronomical usage it means the point directly beneath the observer, the opposite of the zenith, which is not the same thing as the IC; the astrological use of the word for the lower meridian is a loose one, and both terms are found. Like the other three angles it depends entirely on an exact time and place.
Because the Nadir is the exact opposite of the Midheaven, it inherits the same whole-sign-house complication discussed under that entry: in Hellenistic practice using whole-sign houses, the fourth-house cusp is not necessarily the Nadir's own degree but simply the fourth sign counted from the Ascendant, so that, as with the Midheaven and tenth house, the identification of the Nadir with a fixed fourth-house cusp is more characteristic of the quadrant house systems that came to dominate later Western practice than of the earliest surviving technique.