"inner membrane of a calf's stomach," c.1400, probably from an unrecorded O.E. *rynet, related to gerennan "cause to run together," because it makes milk run or curdle; from P.Gmc. *rannijanan, causative of *renwanan "to run" (see
run). Cf. Ger. rinnen "to run," gerinnen "to curdle."