English
synodic month
From synodic + month.
Today it means
noun 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.
Language periods are conventional ranges, not dates for this word.
Etymograph / synodic month