Emily Dickinson Lexicon

RUN'NET, n. [D. runzel, from runnen, ronnen, to curdle; G. rinnen, to curdle, and to run or flow; Sax. gerunnen, coagulated. It is sometimes written Rennet.]

The dried stomach, or the coagulated milk found in the stomachs of calves or other sucking quadrupeds. The same name is given to a liquor prepared by steeping the inner membrane of a calf's stomach in water, and to the membrane itself. This is used for coagulating milk, or converting it into curd in the making of cheese. Encyc.