- noun one of twelve periods which make a year
- The time taken for the Moon to orbit the Earth. Several types of month are defined for different purposes, including the draconitic month, the time the Moon takes to reappear at the same node of its orbit on the celestial equator, which is the most realistic measure and totals 27.21 days, and the sidereal month of 27.32 days, the time the Moon takes to reappear at the same point in the sky relative to the fixed stars. This differs from the draconitic month because of the motion of the Earth and Moon around the Sun. The Anomalistic month of 27.55 days is the total time needed for the Moon’s cycle of slowing and speeding up in its orbit as it is carried nearer and farther from the Earth.
Origin & History of “month”
In ancient times the passing of time was recorded by noting the revolutions of the moon. Consequently prehistoric Indo-European had a single word, *mēnes-, which denoted both ‘moon’ and ‘month’. The romance languages retain it only for ‘month’: Latin mēnsis (source of English menstrual) has given French mois, Italian mese, and Spanish mes. The Germanic languages, however, have kept both, distinguishing them by different forms. In the case of ‘month’, the Germanic word was *mǣnōth, which has differentiated into German monat, Dutch maand, Swedish månad, Danish maaned, and English month.