The name Turkmen first appears in written sources of the 10th century to distinguish those Oghuz groups who migrated south into the Seljuk domains and accepted Islam from those that had remained in the steppe. Gradually, the term took on the properties of an ethnonym and was used exclusively to designate Muslim Oghuz, especially those who migrated away from the Syrdariya Basin. By the 13th century, the term Turkmen supplanted the designation Oghuz altogether. The origin of the word Turkmen remains unclear. According to popular etymologies as old as the 11th century, the word derives from Turk plus the Iranian element manand, and means "resembling a Turk." Modern scholars, on the other hand, have proposed that the element man /men acts as an intensifier and have translated the word as "pure Turk" or "most Turk-like of the Turks."