interlunar
adjective
in·ter·lu·nar ˌin-tər-ˈlü-nər 
variants or less commonly interlunary
ˌin-tər-ˈlü-nə-rē
: relating to the interval between old and new moon when the moon is invisible
Word History
Etymology
probably from Middle French interlunaire, from Latin interlunium interlunar period, from inter- + luna moon — more at lunar
First Known Use
1598, in the meaning defined above