Snitch recruited by copper or keeper (7)
I believe the answer is:
curator
'keeper' is the definition.
(I know that curator is a type of keeper)
'snitch recruited by copper or' is the wordplay.
'snitch' becomes 'rat' (I've seen this in another clue).
'recruited by' means one lot of letters goes inside another.
'copper' becomes 'cu' (chemical symbol).
'cu'+'or'='cuor'
'rat' going within 'cuor' is 'CURATOR'.
(Other definitions for curator that I've seen before include "Museum officer" , "Museum official" , "Museum's administrative head" , "Museum custodian" , "Person in charge of a museum" .)