Nadir

Webster's Dictionary

(1): (n.) The lowest point; the time of greatest depression.

(2): (n.) That point of the heavens, or lower hemisphere, directly opposite the zenith; the inferior pole of the horizon; the point of the celestial sphere directly under the place where we stand.

The Nuttall Encyclopedia

Name given to the part of the heavens directly under our feet, as zenith to that directly over our head.