Answer: SARONIC

AnswerCrossword Clue
SARONIC.... Gulf:
SARONIC... Gulf, Aegean Sea inlet
saronicthe period of 223 synodic months, equaling 6585.32 days or 18 years, 11.32 days (or 10.32 days if 5 leap years occur in the interval), after which eclipses repeat but are shifted 120┬░ west
saronicpertaining to an astronomical cycle