ETYM Old Eng. month, moneth, AS. mônth, mônath; akin to môna moon, and to Dutch maand month, German monat, Old High Germ. mânôd, Icel. mânuthr, mânathr, Goth. męnôths. Related to Moon.
A time unit of 30 days.
Unit of time based on the motion of the Moon around the Earth.
The time from one new or full Moon to the next (the synodic or lunar month) is 29.53 days. The time for the Moon to complete one orbit around the Earth relative to the stars (the sidereal month) is 27.32 days. The solar month equals 30.44 days, and is exactly one-twelfth of the solar or tropical year, the time taken for the Earth to orbit the Sun. The calendar month is a human invention, devised to fit the calendar year.