synodic month

Meanings

1. A month of approximately 29.53 days, measured from a lunar phase until the return of that same phase. The long-term average duration is 29.530 588 days (29 d 12 h 44 min 2.8 s), or about 29 ½ days.
2. The variably cyclic period from one new moon until the next.

Etymology

From synodic + month.