/ Dictionary / Index R rennin: Meaning and Definition of Find definitions for: ren•nin Pronunciation: (ren'in), [key] — n. Biochem. a coagulating enzyme occurring in the gastric juice of the calf, forming the active principle of rennet and able to curdle milk. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: rennin (Thesaurus) Rennie Reno Related Content Daily Word Quiz: panacea Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language