Black cats on island left in large numbers (8)
I believe the answer is:
billions
'large numbers' is the definition.
'billions' can be an answer for 'numbers' (billion is a kind of number). I am not sure about the 'large' bit.
'black cats on island left' is the wordplay.
'black' becomes 'b' (abbreviation as in pencil classifications).
'cats' becomes 'lions' (lion is a kind of cat).
'on' means one lot of letters go next to another.
'island left' becomes 'il' (this could be a standard abbreviation I've not previously seen).
'lions' put after 'il' is 'illions'.
'b'+'illions'='BILLIONS'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for billions that I've seen before include "No bills I turn into vast sums" , "Millions of millions" .)