Imaginary armed revolution fell back on president (9)
I believe the answer is:
dreamlike
'imaginary' is the definition.
(thesaurus)
'armed revolution fell back on president' is the wordplay.
'revolution' is an anagram indicator.
'back' indicates one should take the final letters.
'on' means one lot of letters go next to another.
'president' becomes 'ike' (nickname of Dwight Eisenhower).
The last letter of 'fell' is 'l'.
'armed' anagrammed gives 'dream'.
'dream'+'l'+'ike'='DREAMLIKE'
(Other definitions for dreamlike that I've seen before include "Imagined" , "Illusory" .)