M
Abbreviation with 13 meanings
| Stands for | Meter |
|---|---|
| Meanings | 13 |
| Categories | Units & Measurements, Science & Engineering, Arts & Entertainment, Writing & Everyday |
| Also written | m, M., m. |
M has 13 meanings. The most common are Meter (metric and SI unit) and Million (math); it can also stand for Mega- (million), Milli- (thousandth), Mean (APA style), Molar (moles per liter) and Monday (schedule code), plus 6 more listed below.
Meanings of M at a glance
| # | M stands for | Context |
|---|---|---|
| 1 | Meter | Units & Measurements › Metric and SI Unit |
| 2 | Million | Units & Measurements › Math |
| 3 | Mega- (million) | Units & Measurements › Metric and SI Unit |
| 4 | Milli- (thousandth) | Units & Measurements › Metric and SI Unit |
| 5 | Mean (APA style) | Units & Measurements › Statistics |
| 6 | Molar (moles per liter) | Science & Engineering › Chemistry |
| 7 | Monday (schedule code) | Units & Measurements › Day of the Week |
| 8 | Thousand (Roman numeral M) | Units & Measurements › Math |
| 9 | Mature | Arts & Entertainment › Video Game |
| 10 | Minute (informal) | Units & Measurements › Time |
| 11 | Messier object | Science & Engineering › Astronomy & Space |
| 12 | Married | Writing & Everyday › Genealogy |
| 13 | Monsieur | Writing & Everyday › Title and Honorific |
1. Meter (m)
Units & Measurements · Metric and SI Unit Abbreviations
The SI base unit of length, defined since 1983 as the distance light travels in a vacuum in 1/299,792,458 of a second. It is the everyday length unit in almost every country except the United States and equals about 3.28 feet or 39.37 inches.
Example: The pool is 25 m long, so 40 lengths make a full kilometer.
American English spells it meter; British and most Commonwealth usage prefers metre, keeping meter for measuring devices. The symbol is always a lowercase m with no period. It was first defined in the 1790s as one ten-millionth of the distance from the North Pole to the equator along the meridian through Paris. Standing before another symbol, m becomes the prefix milli-, as in mm.
2. Million
Units & Measurements · Math Abbreviations
Modern shorthand for million in headlines, financial reports, startup funding news and statistics: $5M means five million dollars, and 2.3M views means 2.3 million.
Example: The startup raised $40M in Series B funding led by two venture firms.
Styles vary: the AP Stylebook spells out million ($5 million), The Economist writes 5m, and spreadsheets often use M or MM. The SI prefix mega- (M) also means a million, which reinforces the modern usage. Traditional accounting and the energy industry use M for a thousand, so financial documents should define their units.
3. Mega- (million)
Units & Measurements · Metric and SI Unit Abbreviations
Multiplies a unit by 10^6, one million, as in megawatt, megahertz, megapixel, megabyte and megaton. The capital matters: lowercase m means milli-, one thousandth, so MW and mW differ by a factor of a billion.
Example: The new solar farm will deliver 250 MW of peak capacity to the regional grid.
Named from Greek megas, great. Mega- was in use with the CGS system from the 1870s and became part of SI in 1960. In informal English it is an intensifier ("a mega sale"). Do not confuse the prefix with M for molar concentration in chemistry or with the M meaning a thousand in older business shorthand such as MBH and Mcf.
4. Milli- (thousandth) (m)
Units & Measurements · Metric and SI Unit Abbreviations
Lowercase m in front of a unit symbol divides it by a thousand (10^-3), as in millimeter, milligram, milliliter, millisecond and milliampere. The lowercase form is mandatory, since capital M means mega-, a billion times larger.
Example: The prescription label reads 250 mg twice daily with food.
From Latin mille, thousand; part of the 1795 system. A lone m means meter; m acts as a prefix only when joined to another symbol, as in mm or ms. Clinicians write mcg rather than the micro symbol for micrograms because a handwritten micro sign can be misread as m, a thousandfold dosing error.
5. Mean (APA style)
Units & Measurements · Statistics Abbreviations
In APA-style research writing, an italic M reports the arithmetic mean of a sample, usually paired with SD. It appears in the results sections and tables of psychology, education and social science papers.
Example: Participants in the mindfulness group reported lower stress (M = 2.8, SD = 0.9).
APA style uses M in text and tables and keeps the symbol x̄ (x-bar) for equations, while Greek μ denotes a population mean. In other contexts M means million, thousand or the prefix mega-, so italics and context signal the statistical sense.
6. Molar (moles per liter)
Science & Engineering · Chemistry Abbreviations · also used in measurement
Unit of concentration equal to one mole of solute per liter of solution, written as a capital M after a number, such as 0.1 M HCl. Molarity is the most common way chemists and biologists express solution strength, from 1 M stock buffers to nanomolar drug potencies.
Example: Prepare 500 mL of 0.5 M sodium chloride by dissolving 14.6 g in water and diluting to volume.
Molarity (M) is not the same as molality (m), moles per kilogram of solvent, which does not change with temperature. The SI-preferred notation is mol/L or mol dm-3, but M remains universal in labs. Prefixes give mM (millimolar) and nM (nanomolar); N (normality) is an older related unit.
7. Monday (schedule code)
Units & Measurements · Day of the Week Abbreviations
Single-letter code for Monday in class schedules, gym timetables and transit charts, as in MWF for Monday, Wednesday and Friday sessions.
Example: CHEM 101 Lecture: M W F 10:00 to 10:50, Hall B.
Registrars use single-letter day codes to save space in course listings. Monday is rarely ambiguous because no other English day begins with M. The iCalendar standard for calendar files uses two letters instead, MO, as in BYDAY=MO for a weekly Monday meeting.
8. Thousand (Roman numeral M)
Units & Measurements · Math Abbreviations
In traditional accounting, printing, advertising and the energy industry, M denotes one thousand, from the Roman numeral M and Latin mille. Examples include CPM (cost per mille, per thousand ad impressions), Mcf (thousand cubic feet) and MBH (thousand BTU per hour).
Example: Printing costs $48 per M for the four-color brochure.
This older convention clashes with modern business shorthand in which M means million, so "$5M" in a headline almost always means five million. Bond markets and oil and gas reporting keep M as thousand and MM as million. When the distinction matters, writers spell out "thousand" or use K.
9. Mature
Arts & Entertainment · Video Game Abbreviations
ESRB rating for games suitable for ages 17 and up, which may contain intense violence, blood and gore, sexual content or strong language. Many retailers require ID to buy M-rated games.
Example: Call of Duty is rated M, so his parents had to buy it for him.
Grand Theft Auto, The Last of Us and Mortal Kombat are M-rated. The rating is roughly comparable to an R for films. The 2011 Supreme Court case Brown v. Entertainment Merchants Association struck down a California law restricting sales of violent games to minors.
10. Minute (informal) (m)
Units & Measurements · Time Abbreviations
A single m after a number often means minutes in informal durations, video lengths and timestamps, as in 1h 30m or a 45m workout. Software interfaces, social media, cloud billing and fitness apps use it where space is tight.
Example: Estimated reading time: 7m; video length 12m 40s.
In SI, m strictly means meter, and min is the correct symbol for minute, so formal writing avoids 30m for half an hour. The same letter appears in ISO 8601 durations, where PT1H30M means one hour thirty minutes, while an M before the T means months. Context usually tells whether 5m means five minutes, five meters or five million.
11. Messier object
Science & Engineering · Astronomy & Space Abbreviations
Prefix for objects in Charles Messier's catalogue of 110 nebulae, star clusters and galaxies, written as M plus a number, such as M31 for the Andromeda Galaxy, M42 for the Orion Nebula and M45 for the Pleiades. These are among the brightest and best-known deep-sky targets.
Example: M13, the Great Globular Cluster in Hercules, looks like a fuzzy ball in small telescopes.
Charles Messier, an 18th-century French comet hunter, compiled the list to avoid mistaking these fuzzy objects for comets; his first version appeared in 1774. The final objects were added by later astronomers based on his notes. M1 is the Crab Nebula, the remnant of a supernova seen in 1054.
12. Married (m.)
Writing & Everyday · Genealogy Abbreviations
Records a marriage in genealogies and biographies, often with the spouse's name, date and place, as in "m. 1846 Mary Hale."
Example: Thomas Reed m. (1) 1822 Ann Lowe; m. (2) 1835 Sarah Platt, widow of James Platt.
Numbers in parentheses distinguish successive marriages. British peerage works often use an equals sign for "married," and German genealogies use a symbol of two linked rings. A longer variant is marr. Elsewhere m. can mean male, meter or minute, so context matters.
13. Monsieur (M.)
Writing & Everyday · Title and Honorific Abbreviations
Standard French abbreviation of Monsieur, the courtesy title for a man, used in English writing when referring to French-speaking men, especially in formal or historical contexts.
Example: The minister met M. Dupont, the French ambassador, at the embassy on Tuesday.
In correct French usage the abbreviation is M., not "Mr." or "Mons."; "Mr" is regarded in France as an anglicism. The plural is MM. (Messieurs). Pronounced "muh-SYUR." English-language newspapers that use courtesy titles sometimes apply M. to French officials.
Related abbreviations
More metric and SI unit abbreviations
- kN – Kilonewton
- kt – Kiloton (TNT equivalent)
- L – Liter
- ly – Light-year
- mcg – Microgram
- mg – Milligram
- MKS – Meter-kilogram-second system
- mL – Milliliter
See all 64 metric and SI unit abbreviations →