month

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A unit of time corresponding approximately to one cycle of the moon's phases, or about 30 days or 4 weeks.
2. n. One of the 12 divisions of a year as determined by a calendar, especially the Gregorian calendar. Also called calendar month.
3. n. A period extending from a date in one calendar month to the corresponding date in the following month.
4. n. A sidereal month.
5. n. A lunar month.
6. n. A solar month.
7. idiom. month of Sundays Informal An indefinitely long period of time: It will take you a month of Sundays to chop all that wood.

Century Dictionary and Cyclopedia

1. n. Originally, the interval from one new moon to the next, called specifically a lunar, synodical, or illuminative month. This seldom varies more than a quarter of a day from its mean value, which is 29, 530589 days, or 29 days, 12 hours, 44 minutes, and 2.7 seconds. There are, besides, other periods of the moon which are termed months by astronomers. These are
2. n. One twelfth part of a tropical year, or 30 days, 10 hours, 29 minutes, 3. 8 seconds: called specifically a solar month.
3. n. One of the twelve parts into which the calendar year is arbitrarily divided: called specifically a calendar month. The calendar months are January, 31 days: February, 28 (except in leap-year, when it has 29); March, 31; April 30; May, 31; June, 30; July, 31; August, 31; September, 30; October, 31; November, 30; December, 31.
4. n. At common law and in equity, month has been understood to mean ‘a lunar month,’ which is assumed to be 28 days, except when the contrary appears, and except when used of mercantile transactions, such as negotiable paper, etc. In ecclesiastical law, and now in all cases throughout the United States generally, its legal meaning is ‘a calendar month,’ except when the contrary appears. For the purpose of calculating interest, a month is generally considered the twelfth part of a year, and as equivalent to 30 days.
5. n. plural Same as menses. Minsheu; Cotgrave. Abbreviated mo.

Wiktionary

1. n. A period into which a year is divided, historically based on the phases of the moon. In the Gregorian calendar there are twelve months: January, February, March, April, May, June, July, August, September, October, November and December.
2. n. A period of 30 days, 31 days, or some alternation thereof.
3. n. obsolete, in the plural A woman's period; menstrual discharge.

GNU Webster's 1913

1. n. One of the twelve portions into which the year is divided; the twelfth part of a year, corresponding nearly to the length of a synodic revolution of the moon, -- whence the name. In popular use, a period of four weeks is often called a month.

WordNet 3.0

1. n. a time unit of approximately 30 days
2. n. one of the twelve divisions of the calendar year