pronephros
noun
pro·neph·ros (ˌ)prō-ˈne-frəs 
-ˌfräs
: either member of the first and most anterior pair of the three successive paired vertebrate renal organs that functions in the adults of amphioxus and some lampreys, functions temporarily in larval fishes and amphibians, and is present but nonfunctional in embryos of reptiles, birds, and mammals compare mesonephros, metanephros
pronephric
(ˌ)prō-ˈne-frik
adjective 
Word History
Etymology
New Latin, from Greek pro- + nephros kidney — more at nephritis
First Known Use
1877, in the meaning defined above
Medical Definition
pronephros
noun
pro·neph·ros (ˈ)prō-ˈnef-rəs, -ˌräs
plural pronephroi -ˌrȯi
: either member of the first and most anterior pair of the three paired vertebrate renal organs that functions in the adults of amphioxus and some lampreys, functions temporarily in larval fishes and amphibians, and is present but nonfunctional in embryos of reptiles, birds, and mammals compare mesonephros, metanephros