Source : Webster's Revised Unabridged Dictionary (1913)

Kidney \Kid"ney\, n.; pl. {Kidneys}. [OE. kidnei, kidnere, from
   Icel. koi?r belly, womb (akin to Goth. gipus, AS. cwip womb)
   + OE. nere kidney; akin to D. nier, G. niere, OHG. nioro,
   Icel. n?ra, Dan. nyre, Sw. njure, and probably to Gr. (?) Cf.
   {Kite} belly.]

Source : WordNet®

kidney
     n : either of two bean-shaped excretory organs that filter
         wastes (especially urea) from the blood and excrete them
         and water in urine; urine passes out of the kidney
         through ureters to the bladder