[AS. monadh, from mona, the moon.] The twelfth part of the calendar year - popularly the space of four weeks. The calendar month has 30 or 31 days, except February, which has 28, and in a leap year 29; the lunar month is 29 days 12 hrs. 44 min. 2.684 sec ; and the side-real month is 27 days 7 hrs. 43 min. 11.545 sec.