Rennin \Ren"nin\ (r[e^]n"n[i^]n), n. (Biochem.) A milk-clotting enzyme obtained from the true stomach (abomasum) of a suckling calf. Mol. wt. about 31,000. Also called {chymosin}, {rennase}, and {abomasal enzyme}. --[Merck Man. 11] [1913 Webster]