period of time,
time period,
period an amount of time; "a time period of 30 years"; "hastened the period of time of his recovery"; "Picasso's blue period"
A month is a unit of time, used with calendars, which was first used and invented in Egypt, as a natural period related to the motion of the Moon; month and Moon are cognates. The traditional concept arose with the cycle of moon phases; such months are synodic months and last approximately 29.53 days. From excavated tally sticks, researchers have deduced that people counted days in relation to the Moon's phases as early as the Paleolithic age.
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month A period into which a year is divided, historically based on the phases of the moon. In the Gregorian calendar there are twelve months.
month A period of time lasting approximately thirty days.