Feeling no end upset, being catty (6)
I believe the answer is:
feline
'being catty' is the definition.
(thesaurus)
'feeling no end upset' is the wordplay.
'no end' means to remove the last letter.
'upset' is an anagram indicator.
'feeling' with its final letter taken off is 'feelin'.
'feelin' is an anagram of 'FELINE'.
(Other definitions for feline that I've seen before include "Pertaining to cats" , "Relating to cats" , "Of or like cats" , "(Relating to a) cat" , "Scots dish" .)