One is about to make a racket (5)
I believe the answer is:
noise
'make a racket' is the definition.
(thesaurus)
'one is about' is the wordplay.
'about' indicates anagramming the letters.
'one'+'is'='oneis'
'oneis' with letters rearranged gives 'NOISE'.
'to' acts as a link.
(Other definitions for noise that I've seen before include "Hum" , "Sound of any kind" , "Loud or disturbing sound" , "interference" , "Uproar" .)