rennin

ren·nin

noun \ˈren-ən\

Definition of RENNIN

: a crystallizable enzyme that coagulates milk, that occurs especially with pepsin in the gastric juice of young animals and is obtained as a yellowish powder, grains, or scales usually by extraction of the mucous membrane of the fourth stomach of calves, and that is used chiefly in making cheese and casein for plastics—called also chymosin