ISIL

When this organisation first started to appear in the news media, it was known as ISIS: the Islamic State in Iraq and Syria. Apparently the word used in Arabic for the 'Syria' part of the name is used to denote Damascus, and can also mean Greater Damascus, which is synonymous with the region that's known in English as The Levant; and that's why ISIS became ISIL (which my source – see below – described as "the US–preferred acronym").

The name Islamic State in Iraq and the Levant (ISIL) translates into Arabic as 'al–dowla al–islaamiyya fii–il–i'raaq wa–ash–shaam'. Obviously this has been transliterated into Roman script; the D in 'Daesh' comes from al–dowla, the A from al–islaamiyya, the E from i'raaq, and the SH from shaam. (There was a fuller explanation in the Internet article referenced below.)

The name Daesh is seen by those opposed to "the so–called Islamic State" as "a challenge to their legitimacy: a dismissal of their aspirations to define Islamic practice, to be 'a state for all Muslims' and – crucially – as a refusal to acknowledge and address them as such".

I transcribed this information in 2017 from a well–informed, but long–winded, article on a website called The Free Word. Unfortunately this seems to be no longer available.