trinundinus

trĭnundĭnus, a, um, adj. [tres nundinae], of or belonging to three weekly market-days (very rare):

trinundino die,

after seventeen days, Macr. S. 1, 16, 34; v. trinus, II. B., and nundinus, III. — Hence, adv.: trĭnundĭnō, = trinundino die, Macr. S. 2, 13, 7.