Lewis Short
(adjective) : inter-menstrŭus, a, um
* Between two months: lunā intermenstruā,i. e. at the time of new moon,Plin. 18, 32, 75, § 322.—Subst.: intermenstrŭum, i. n. (sc. tempus), the new moon, time of new moon, Varr. R. R. 1, 37, 1; Cic. Rep. 1, 16, 25: tempore intermenstrui,Amm. 20, 3, 11.
Charlton T. Lewis, Charles Short, A Latin Dictionary