interlunar

Of or relating to the four-day period between the old and new moon when the moon is not readily visible.

Pertaining to the moon’s monthly interval of invisibility; between the periods of moonlight: as, interlunar nights. The interlunar cave is the place of seclusion into which the moon was anciently supposed to retire at such times.

Belonging or pertaining to the time when the moon, at or near its conjunction with the sun, is invisible.

Of the four-day period between an old moon and a new moon, when it is not visible