Meaning

• The point of the celestial sphere, directly opposite the zenith; inferior pole of the horizon; point of the celestial sphere directly under the place of observation.

• The lowest point; time of greatest depression.

• 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."

• An empty box added beneath a full one in a beehive to give the colony more room to expand or store honey.

Meaning

• To extend (a beehive) by adding an empty box at the base.