Definition of "tumen"

The largest unit was the tumen, equivalent to a division: 10,000 men in principle (and sometimes less). An army was made up of two to four tumen, each composed of ten times a thousand men (the equivalent of a regiment), and each regiment of ten times a hundred men (the equivalent of a squadron), ten times ten men.

2004, Gerard Chaliand, Nomadic Empires: From Mongolia to the Danube, page 65