A classical Greek name for the number 104=10000, or a group of 10000 people etc.
As useful as a name for this number would be (the Chinese and Japanese give ten thousand its own name), in English we call the number 10,000 "ten thousand", and use "myriad" only to mean "very many". In English numbering system, digits are handled in group of three, hence there is no need for the word for 10000. In Asian numbering system, digits are handled in group of four, e.g. 30000 is called three myriad in Chinese or Japanese, (3,0000). 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 myraid i.e. 1,000,000 vs 100,0000.
See more detailed discussion on Chinese numerals