"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."