Every cat's possession upset Lenin and Burl (4,5)
I believe the answer is:
nine lives
'every cat's possession' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'upset lenin and burl' is the wordplay.
'upset' says the letters should be written in reverse.
'and' is a charade indicator (letters next to each other).
'burl' becomes 'ives' (I've seen this in another clue).
'lenin' reversed gives 'ninel'.
'ninel'+'ives'='NINE LIVES'
Can you help me to learn more?
(Another definition for nine lives that I've seen is " Number of existences attributed to a cat".)