Transoxiana

Wikipedia: "Greater Khorāsān or Khorāsān or Khurāsān is a historical eastern region in the Iranian Plateau between West and Central Asia that encompasses western Afghanistan, northeastern Iran, the eastern halves of Turkmenistan and Uzbekistan, western Tajikistan, and portions of Kyrgyzstan and Kazakhstan."

The names in the map are in German because I stole it from the internet. Khorasan is where ISIS-K gets its K from. The K doesn't even make sense, because the letter combination 'kh' is used to transliterate a 'ch' as in the Scottish 'loch', found in pretty much every language except for English. And we don't say Lok Ness, do we? (and if we do, we are saying it wrong.) So it should be ISIS-Kh instead, but most people would probably find that even more confusing.

The real marvel here is of course Transoxania (also called Transoxiana). Who had ever heard of a place like that.