Church group attached to old cat (6)
I believe the answer is:
ocelot
'cat' is the definition.
(type of wild cat)
'church group attached to old' is the wordplay.
'church' becomes 'CE' (abbreviation for Church of England).
'group' becomes 'lot'.
'attached to' says to put letters next to each other.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'ce'+'lot'='celot'
'celot' after 'o' is 'OCELOT'.
(Other definitions for ocelot that I've seen before include "Spotted New World feline" , "Big cat" , "Wild cat, native to Central and South America - loo etc (anag)" , "Small leopardlike cat" , "Wildcat -- loo etc (anag)" .)