Kidney
Kidney (kid"ny) , noun
[Old English kidnei, kidnere, from Icelandic koier belly, womb (akin to Gothic gipus, Anglo-Saxon cwiþ womb) + Old English nere kidney; akin to Dutch nier, German niere, Old High German nioro, Icelandic nȳra, Danish nyre, Swedish njure, and probably to Greek nefro`s Compare Kite belly.]
In man and in other mammals there are two kidneys, one on each side of vertebral column in the back part of the abdomen, each kidney being connected with the bladder by a long tube, the ureter, through which the urine is constantly excreted into the bladder to be periodically discharged.
This use of the word perhaps arose from the fact that the kidneys and the fat about them are an easy test of the condition of an animal as to fatness. “Think of that, -- a man of my kidney; --... as subject to heat as butter.”