- any of the twelve parts, as January or February, into which the calendar year is divided.
- the time from any day of one calendar month to the corresponding day of the next.
- a period of four weeks or 30 days.
- one-twelfth of a solar or tropical year.
- the period of a complete revolution of the moon around the earth, as the period between successive new moons (synodic month ), equal to 29.531 days, or the period between successive conjunctions with a star (sidereal month ), equal to 27.322 days, or the period between successive perigees (anomalistic month ), equal to 27.555 days, or the period between successive similar nodes (nodical month, or draconic month ), equal to 27.212 days.
- an unusually long period of time of indefinite length: I haven't seen him for months.
- one of the twelve divisions (calendar months) of the calendar year
- a period of time extending from one date to a corresponding date in the next calendar month
- a period of four weeks or of 30 days
- 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)
- 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)
- the period of time (lunar or synodic month) taken by the moon to make one complete revolution around the earth, measured between two successive new moons; 29.530 59 days (approximately 29 days, 12 hours, 44 minutes, 3 seconds)
- a long unspecified period
