Uproar is interrupting one terribly (5)
I believe the answer is:
noise
'uproar' is the definition.
(thesaurus)
'is interrupting one terribly' is the wordplay.
'interrupting' means one lot of letters goes inside another.
'terribly' is an anagram indicator.
'one' anagrammed gives 'noe'.
'is' inserted inside 'noe' is 'NOISE'.
(Other definitions for noise that I've seen before include "Sound of any kind" , "Racket, din" , "Loud or unpleasant sound" , "Loud sound; bruit" , "Unstructured sound" .)