An organ in your lower back that allows you to expel waste by creating urine is an example of a kidney.
A person of the same kidney.
Origin of kidney
- Middle English kidenei
From American Heritage Dictionary of the English Language, 5th Edition
- From Middle English kednei, kidenei, from earlier kidnēre, kidenēre (“kidney”). Of obscure origin and formation. Probably a compound consisting of Middle English *kid, *quid (“belly, womb”), from Old English cwiþ, cwiþa (“belly, womb, stomach”) + Middle English nēre (“kidney”), from Old English *nēora (“kidney”), from Proto-Germanic *neurô (“kidney”), from Proto-Indo-European *negʷh-r- (“kidney”). If so, then related to Scots nere, neir (“kidney”), Dutch nier (“kidney”), German Niere (“kidney”), Danish nyre (“kidney”), Swedish njure (“kidney”).
- Alternate etymology traces the first element to Old English cēod, codd (“sack, scrotum”), from Proto-Germanic *keudō (“sack”) as the terms for testicle and kidney were often interchangeable in Germanic (compare Old High German nioro (“kidney", also "testicle”), Old Swedish vig-niauri (“testicle”). More at codpiece.