one of the twelve divisions (calendar months) of the calendar year
2.
a period of time extending from one date to a corresponding date in the next calendar month
3.
a period of four weeks or of 30 days
4.
the period of time (tropical month) taken by the moon to return to the same longitude after one complete revolution around the earth; 27.321 58 days (approximately 27 days, 7 hours, 43 minutes, 4.5 seconds)
5.
the period of time (sidereal month) taken by the moon to make one complete revolution around the earth, measured between two successive conjunctions with a distant star; 27.321 66 days (approximately 27 days, 7 hours, 43 minutes, 11 seconds)
6. Also called: lunation
the period of time (lunar or synodic month) taken by the moon to make one complete revolution around the earth, measured betweentwo successive new moons; 29.530 59 days (approximately 29 days, 12 hours, 44 minutes, 3 seconds)
7. a month of Sundays
▶ Related adjective: mensal
Word origin
Old English mōnath; related to Old High German mānōd, Old Norse mānathr; compare Gothic mena moon