In the context of numeric naming systems forpowers of ten,myriad is the quantity ten thousand (10,000). Idiosyncratically, inEnglish, myriad describes a group of things as havingindefinitely large quantity.^[1]

Myriad derives from theancient Greek for ten thousand (μυριάς,myrias) and is used with this meaning inliteral translations fromGreek,Latin orSinospheric languages (Chinese,Japanese,Korean, andVietnamese), and in reference to ancientGreek numerals.

The term myriad is also used in the form "a myriad" for a 100 km × 100 km square (10,000 km) the grid size of the BritishOrdnance Survey National Grid and the USMilitary Grid Reference System. It contains 100hectads.^{[citation needed]}

TheAegean numerals of theMinoan andMycenaean civilizations included a symbol composed of a circle with four dashes𐄫 to denote tens of thousands.^[2]

In classicalGreek numerals, myriad was written as a capitalmu:Μ. To distinguish this numeral from letters, it was sometimes given anoverbar:M. Multiples were written above this sign. For example${\displaystyle \stackrel{\delta \varphi \pi \beta }{\mathrm{M}}}$  is 4,582×10,000 or 45,820,000.

The etymology ofmyriad is uncertain. It has been variously connected toPIE*meu- ("damp") in reference to the waves of the sea and to Greekmyrmex (μύρμηξ, "ant") in reference to their swarms.^[3]

In hisSand Reckoner,Archimedes used "myriad myriad" (MM, one hundred million) as the basis for a numeration system of large powers of ten, which he used to count grains of sand.^[4]

Myriad may be used either as anadjective (there are myriad people outside) or as anoun (there is a myriad of people outside),^[5] but there are small differences. The former might imply that it is a diverse group of people whereas the latter usually does not.

Despite its usually meaning (a large, unspecified quantity),myriad is sometimes used in English to mean ten thousand although usually restricted to translation from other languages likeancient Greek andChinese where quantities are grouped by 10,000. Such use permits the translator to remain closer to the original text and avoid unwieldy mentions of "tens of thousands". For example, "the original number of the crews supplied by the several nations I find to have been twenty-four myriads"^[6] and "What is the distance between one bridge and another? Twelve myriads ofparasangs".^[7]

Most European languages include a variation ofmyriad with a similar meaning to the English word.

Additionally, theprefixmyria- indicating multiplication times ten thousand (×10⁴), was part of the originalmetric system adopted byFrance in 1795.^[8] Although it was not retained after the 11thCGPM conference in 1960,myriameter is sometimes still encountered as a translation of theScandinavian mile (Swedish &Norwegian: mil) of 10 kilometers (6.21 mi), or in some classifications of wavelengths as the adjectivemyriametric. Themyriagramme (10 kg) was a French approximation of theavoirdupoisquartier of 25 pounds (11 kg) and themyriaton appears inIsaac Asimov'sFoundation novel trilogy.

Inmodern Greek, the word "myriad" is rarely used to denote 10,000, but a million isekatommyrio (εκατομμύριο,lit. 'hundred myriad') and athousand million isdisekatommyrio (δισεκατομμύριο,lit. 'twice hundred myriad').

InEast Asia, the traditional numeral systems ofChina,Korea, andJapan are alldecimal-based but grouped into ten thousands rather than thousands. Thecharacter for myriad is萬 intraditional script and万 insimplified form in bothmainland China andJapanese; its pronunciation varies between languages (Mandarin:wàn,Hakka:wan⁵,Minnan:bān,Cantonese:maan⁶,Japanese andKorean:man,Vietnamese:vạn,Thai: หมื่นmuen andKhmer: ម៉ឺនmeun).^{[citation needed]}

Because of this grouping into fours, higher orders of numbers are provided by thepowers of 10,000 rather than 1,000: In China, 10,000² was萬萬 in ancient texts but is now called億 and sometimes written as 1,0000,0000; 10,000³ is 1,0000,0000,0000 or兆; 10,000⁴ is 1,0000,0000,0000,0000 or京; and so on. Conversely, Chinese, Japanese, and Korean generally do not have native words for powers of one thousand: what is called "one million" in English is "100萬" (100 myriad) in theSinosphere, and "one billion" in English is "十億" (tenmyllion) or "十萬萬" (ten myriad myriad) in the Sinosphere. Unusually, Vietnam employs its former translation of兆,một triệu, to mean 1,000,000 rather than the Chinese figure. Similarly, the Chinese government has adapted the word兆 to mean the scientific prefixmega-, but transliterations are used instead forgiga-,tera-, and other larger prefixes. This has caused confusion in areas closely related to China such asHong Kong andMacau, where兆 is still largely used to mean 10,000³.^{[citation needed]}

萬 and万 are also frequently employed colloquially in expressions,clichés, andchengyu (idioms) in the senses of "vast", "numerous", "numberless", and "infinite". Askeleton key is a万能钥匙 ("myriad-use key"),^[9] theemperor was the "lord of myriadchariots" (萬乘之主),^[10] theGreat Wall is called万里长城 ("Myriad-mile Long Wall"),Zhu Xi's statement月映万川 ("the moon reflects in myriad rivers") had the sense of supporting greaterempiricism inChinese philosophy,^[11] and Ha Qiongwen's popular 1959propaganda poster毛主席万岁, meaning "Long liveChairmanMao", literally reads as "[May] Chairman Mao [live to be]10,000 years old".^[12]

A similar term is theOld Turkic wordtümän,^[13] whose variant forms remain in use for "ten thousand" among modernMongolian,Turkish.^[14][15] According toSir Gerard Clauson (1891–1974), it was likely borrowed fromTokhariantmān, which may have been borrowed in turn fromOld Chinesetman 萬 >wan.^[16]

InHebrew the word רבבה (pronounced "revava") means 10,000, and is the highest number represented in Hebrew. Its sources go back to biblical times.^[17] Its usage became very rare after the 19th century. The term 60 ריבוא ("60 ribo"), which literally stands for 600,000 is used several times in the bible to denote "a very large undefinitive number".^{[citation needed]}

  The dictionary definition ofmyriad at Wiktionary

• -yllion – Mathematical notation
• Indian numbering system – Indian convention of naming large numbers
• Long and short scale – Two meanings of "billion" and "trillion"Pages displaying short descriptions of redirect targets
• Names of large numbers