means The nephron is the tiny functional unit of the kidney that filters blood, reclaims what the body needs, and sends the rest off as urine — and you have roughly a million of them per kidney.

from Straight from the Greek nephros, meaning kidney — the same root that gives us nephritis (kidney inflammation) and nephrology (the study of kidneys). The diminutive -on ending lends it the feel of a small unit or particle, fitting for the kidney's microscopic working part. The term entered scientific anatomy in the early 20th century as physiologists mapped the kidney's inner machinery.