Firm hug can end upset (9)
I believe the answer is:
unchanged
'firm' is the definition.
(thesaurus)
'hug can end upset' is the wordplay.
'upset' indicates anagramming the letters.
'hug'+'can'+'end'='hugcanend'
'hugcanend' with letters rearranged gives 'UNCHANGED'.
(Other definitions for unchanged that I've seen before include "Unaltered" , "Remaining in an original state" , "Not altered" .)