noun

1. 1. the membrane lining the stomach of an unweaned animal, esp. the fourth stomach of a calf
   2. the contents of such a stomach
2. 1. an extract of this membrane or of the stomach contents, containing rennin and used to curdle milk, as in making cheese or junket
   2. any substance used to curdle milk
3. rennin

Etymology: ME rennen, to cause to coagulate < OE gerennan < ge-, together (see co-) + Gmc *rannjan, to cause to run < base of *rinnan (> run) + *-jan, caus. suffix