rennet
ren.net \'ren-*t\ n [ME, fr. (assumed) ME rennen to cause to coagulate, fr. OE gerennan], fr. ge- together + (assumed) OE rennan to cause to run; akin to OHG rennen to cause to run, OE rinnan to run - more at CO-, RUN 1a: the contents of the stomach of an unweaned animal (as a calf) 1b: the lining membrane of a stomach (as the fourth of a ruminant) used for curdling milk; also : a preparation of the stomach of animals used for this purpose 2a: RENNIN 2b: a substitute for rennin