- (astronomy) The axis of a projected conical shadow; the direction of the force of gravity at a location; down.
"The nadir of the sun is the axis of the shadow projected by the Earth."
- (figuratively) The lowest point; time of greatest depression.
- The point of the celestial sphere, directly opposite the zenith; inferior pole of the horizon; point of the celestial sphere directly under the place where we stand.
- (beekeeping, archaic) An empty box added beneath a full one in a beehive to give the colony more room to expand or store honey.
- (transitive, beekeeping) To extend (a beehive) by adding an empty box at the base.