lunar month

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The average time between successive new or full moons, equal to 29 days, 12 hours, 44 minutes. Also called synodic month.

Wiktionary

1. n. a period from one new moon until the next.
2. n. a synodic month of approximately 29.53 days, measured from a lunar phase until the return of that same phase.
3. n. a sidereal month of approximately 27.32 days, the length of time taken by the moon in its orbit about the Earth to return to the same point as viewed against the background of stars.

GNU Webster's 1913

1. adj. See Month.
2. n. the period of one revolution of the moon, particularly a synodical revolution; but several kinds are distinguished, as the synodical month, or period from one new moon to the next, in mean length 29 d. 12 h. 44 m. 2.87 s.; the nodical month, or time of revolution from one node to the same again, in length 27 d. 5 h. 5 m. 36 s.; the sidereal, or time of revolution from a star to the same again, equal to 27 d. 7 h. 43 m. 11.5 s.; the anomalistic, or time of revolution from perigee to perigee again, in length 27 d. 13 h. 18 m. 37.4 s.; and the tropical, or time of passing from any point of the ecliptic to the same again, equal to 27 d. 7 h. 43 m. 4.7 s.

WordNet 3.0

1. n. the period between successive new moons (29.531 days)