Old fool captures Eastern cat (6)
I believe the answer is:
ocelot
'cat' is the definition.
(type of wild cat)
'old fool captures eastern' is the wordplay.
'old' becomes 'o' (abbreviation).
'fool' becomes 'clot' (I've seen this before).
'captures' means one lot of letters goes inside another.
'eastern' becomes 'e'.
'clot' enclosing 'e' is 'celot'.
'o'+'celot'='OCELOT'
(Other definitions for ocelot that I've seen before include "Leopard-like cat of S America" , "Feline of South and Central America" , "Small leopardlike cat" , "Yellow-black striped and spotted cat" , "Big cat" .)