Etymology
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kidney (n.)
early 14c., kidenere, a word of unknown origin, perhaps a compound of Old English cwið "womb" (see chitterlings) + ey "egg" (see egg (n.)) in reference to the shape of the organ. Figurative sense of "temperament" is from 1550s. Kidney-bean is from 1540s, so called for its shape.
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nephro- 

before vowels nephr-, word-forming element meaning "kidney, kidneys," from Greek nephros "a kidney" (plural nephroi), from PIE *negwhro- "kidney" (source also of Latin nefrones, Old Norse nyra, Dutch nier, German Niere "kidney").

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nephrology (n.)

"scientific study of the kidney," 1839, from nephro- "kidney" + -logy. Related: Nephrologist.

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nephrectomy (n.)

"excision of a kidney," 1880, from nephro- "kidney" + -ectomy "a cutting out."

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nephrolithiasis (n.)

"the formation of kidney stones," 1837, probably from German, from nephro- "kidney" + lithos "stone" (see litho-) + -iasis "pathological or morbid condition."

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nephron (n.)

"a filtration unit of the kidney," 1932, from German nephron (1924), from Greek nephros "kidney" (see nephro-).

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frijoles (n.)
Mexican kidney beans, 1570s, from Spanish frijoles (plural) "beans," from Latin phaseolus, phaselus "kidney bean," from Greek phaselos a name for a kind of bean.
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reniform (adj.)

in science, "having the form or shape of a (human) kidney," 1753, from Latin renes "kidneys" (see renal) + -form.

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nephridium (n.)

(plural nephridia), "sexual or renal organ of mollusks," 1848, Modern Latin, from Greek diminutive of nephros "kidney" (see nephro-).

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epinephrine (n.)
"adrenaline," 1883, from epi- "upon" + Greek nephros "kidney" (see nephron) + chemical suffix -ine (2). So called because the adrenal glands are on the kidneys.
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