1. A unit of time corresponding approximately to one cycle of the moon's phases, or about 30 days or 4 weeks.
2. One of the 12 divisions of a year as determined by a calendar, especially the Gregorian calendar. Also called calendar month.
3. A period extending from a date in one calendar month to the corresponding date in the following month.
4. A sidereal month.
5. A lunar month.
6. A solar month.
month of Sundays Informal
An indefinitely long period of time: It will take you a month of Sundays to chop all that wood.
[Middle English moneth, month, from Old English mōnath; see mē-2 in the Appendix of Indo-European roots.]
Usage Note: The singular noun month, preceded by a number and a hyphen, is used as a compound adjective: a three-month vacation. The plural possessive form without a hyphen is also standard: a three months' vacation.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.