One who retains magnetic influence (6)
I believe the answer is:
keeper
This clue could be a double definition.
'one who retains' is the first definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'magnetic influence' is the second definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
Can you help me to learn more?
(Other definitions for keeper that I've seen before include "stockist" , "Zoo worker" , "Football or cricket player" , "Animal custodian; plain ring" , "Zoo official" .)