Lewis & Short

internundĭnĭum and internun-dĭnum, ĭi, n. [inter-nundinae], the space of time between two nundinae, Mar. Victorin. p. 2469 P.: quoties rusticus internundino barbam radiebat, Varr. ap. Non. 214, 28; Macr. S. 1, 16, 34.