Catholic in with another crowd to see magic (10)
I believe the answer is:
witchcraft
'magic' is the definition.
(witchcraft is a kind of magic)
'catholic in with another crowd to see' is the wordplay.
'catholic' becomes 'c' (abbreviation as in RC for Roman Catholic).
'in' is an insertion indicator.
'another crowd' becomes 'raft' (both can mean a large amount. I am not sure about the 'another' bit.).
'to' says to put letters next to each other (I've seen this in other clues).
'see' becomes 'c' (the word for the letter, according to Chambers).
'c' placed into 'with' is 'witch'.
'raft' after 'c' is 'craft'.
'witch'+'craft'='WITCHCRAFT'
(Other definitions for witchcraft that I've seen before include "Magic" , "[OBI], say" , "Sorcery skill" , "broomstick?" , "Supernatural power" .)