Myriad

As useful as a name for this number would be (the Chinese, and Japanese, and Korean give ten thousand its own name), in English the number 10,000 is simply called "ten thousand", and use "myriad" only to mean "very many". In Mandarin, 10,000 is Wan (萬 / 万). In Japanese and Korean, 10,000 is Man (万); 100,000,000 (10,000²) in Japanese is Oku and in Korean is Eok (pronounced awk).

In English numbering system, digits are handled in group of three (in thousands), hence there is no need for the word for 10000. In Asian numbering system, digits are handled in group of four (in myriad), e.g. 30000 is called three myriad in Chinese or Japanese, (30,000 - called San-Man or 3-Man in Japanese). On the contrary but for the same reason, the word million has no place in Chinese or Japanese language. The quantity of million is expressed as hundred myriad i.e. 1,000,000 vs 100 * 10,000.

Modern Greek still uses the myriad, but also uses the million. One million is ekatommurio; one billion is not trismurio but disekatommurio.

See more detailed discussion on Chinese numerals