Kitty met an awful arse (9)
I believe the answer is:
fundament
'arse' is the definition.
(synonyms)
'kitty met an awful' is the wordplay.
'kitty' becomes 'fund' (fund or money for a particular purpose).
'awful' indicates anagramming the letters.
'met'+'an'='metan'
'metan' with letters rearranged gives 'ament'.
'fund'+'ament'='FUNDAMENT'
(Other definitions for fundament that I've seen before include "seat" , "Underlying basis - foundation" , "bottom" .)