Copper's right to hold book on punter (8)
I believe the answer is:
customer
'punter' is the 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?
'copper's right to hold book' is the wordplay.
'copper's' becomes 'cu's' (chemical symbol).
'right' becomes 'r' (common abbreviation).
'to hold' means one lot of letters goes inside another.
'book' becomes 'tome' (a tome is a book).
'cus'+'r'='cusr'
'cusr' enclosing 'tome' is 'CUSTOMER'.
'on' acts as a link.
Can you help me to learn more?
(Other definitions for customer that I've seen before include "The one who pays is always right" , "Buyer of goods or services" , "Shopper (or now rail passenger!)" , "Regular" , "'Buyer, client (8)'" .)