"According to multiple reports , the Islamic State
loathes the name . There have been reports of the
Islamic State threatening to cut out the tongues
of anyone who used the phrase publicly, perhaps due
to the word ' s similarity to another Arabic word , ﺩﻋﺲ,
or Das , which means to trample down or crush. The
word "Daeshi " is used as an insult by anti -Islamic
State groups ..."
https://www.washingtonpost.com/news/worldviews/wp/2014/12/05/daesh-john-kerry-starts-calling-the-islamic-state-a-name-they-hate/