lunar month

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The average time between successive new or full moons, equal to 29 days, 12 hours, 44 minutes.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a period from one new moon until the next.
• noun a synodic month of approximately 29.53 days, measured from a lunar phase until the return of that same phase.
• noun 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.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the period between successive new moons (29.531 days)