m

• 英文字母表的第十三个字母，为辅音字母，表示双唇鼻音 /m/。也用作罗马数字 1000、中号（M）、米（长度单位）、地铁或高速公路以及序列中的第十三个。

The thirteenth letter of the English alphabet and the tenth consonant, representing the voiced bilabial nasal sound /m/. As a grapheme, 'M' is produced by pressing the lips together and allowing air to pass through the nose with vocal cord vibration. It is one of the most frequently used letters in English. It functions as the Roman numeral for 1000, an abbreviation for medium size, a designation for motorway or metro, a symbol for meter, and the thirteenth item in a sequence.

1. The thirteenth letter of the English alphabetA1formal

   The uppercase or lowercase character (M, m) that constitutes the thirteenth symbol in the Latin-based English alphabet, classified as a consonant. It represents a voiced bilabial nasal sound produced with both lips closed and the velum lowered, allowing air to resonate through the nasal cavity. It is one of the most common consonants in English and is one of the few sounds that can be sustained indefinitely like a vowel.

   英文字母第十三个字母

   • The word 'mother' begins and ends with the letter M.
   • Humming the sound 'mmm' is one of the first sounds babies make.
   • She wrote a capital M with two upward strokes and two downward strokes.
   • In the NATO phonetic alphabet, M stands for 'Mike'.
   • The letter M is often silent in the middle of words like 'mnemonic'.

2. The Roman numeral for 1000A2formal

   The symbol M used in the Roman numeral system to represent the cardinal number one thousand (mille in Latin). It serves as the largest standard single-character numeral and is used in combination with other symbols for years, large numbers, and formal designations. It is widely encountered in historical dates, monumental inscriptions, and the names of significant events.

   罗马数字1000

   • The year 2025 in Roman numerals is written as MMXXV.
   • The Roman numeral M represents the Latin word 'mille' for thousand.
   • The ancient monument was built around the year M.
   • The Super Bowl in the year 2000 was designated Super Bowl MM.
   • The abbreviation for million in finance is often a double M, as in M and M.

3. An abbreviation for medium sizeA1informal

   The letter M used as a standard label in clothing, beverages, and product sizing to indicate a medium size, typically positioned between small (S) and large (L). It represents the middle or average option in a range of available sizes or capacities. The term is a staple in retail, food service, and e-commerce.

   中号（M）

   • I usually wear a size M in t-shirts.
   • Can I get a medium popcorn and a M soda, please?
   • The sweater is available in S, M, and L sizes.
   • She ordered a medium coffee, marked as M on the cup.
   • The shirt runs large, so even the M fits loosely.

4. The symbol for meter in the metric systemA2formalscientific

   The lowercase letter m used as the international standard symbol for the meter, the base unit of length in the International System of Units (SI). It is defined by the distance light travels in a vacuum in 1/299,792,458 of a second. It is used globally in scientific contexts, engineering, and everyday measurement in metric-using countries.

   米（长度单位）

   • The room was 5 m long and 4 m wide.
   • Usain Bolt holds the world record for the 100 m sprint.
   • The speed limit is 50 km/h, equivalent to roughly 14 m/s.
   • The mountain peak is over 8000 m above sea level.
   • The building's height is precisely 150 m.

5. An abbreviation for motorway or metro transitB1informalbritish

   The letter M used as a common abbreviation for 'motorway' or 'metro' in transportation contexts. In the UK and Ireland, 'M' followed by a number designates major controlled-access highways. In many global cities, 'M' identifies metro or subway systems on maps and signage, providing an intuitive visual cue for rapid transit.

   高速公路或地铁

   • We took the M25 motorway to avoid the city center.
   • The M1 is one of the oldest motorways in England.
   • Look for the red M sign to find the metro entrance.
   • Traffic on the M6 was at a standstill due to an accident.
   • The Paris Metro is identified by a distinctive M logo.