noun

1. any of the main parts (usually twelve) into which the calendar year is divided
   also calendar month
2. 1. the time from any date of one month to the corresponding date of the next
   2. a period of four weeks or 30 days
3. the period of a complete revolution of the moon around the earth with respect to some object; esp.,
   1. the period (synodic month) marked by two successive lunar conjunctions with the sun, equal on the average to 29.53 days: also called lunar month
   2. the sidereal month
4. one twelfth of the solar year
   in full solar month

Etymology: ME < OE monath, akin to Ger monat, ON manuthr < Gmc *menōth- < IE *mēnōt, month, moon, var. of mēn: see moon