Merchant's arrow sent up over monarch (6)
I believe the answer is:
trader
'merchant's' is the definition.
(trader is a kind of merchant)
'arrow sent up over monarch' is the wordplay.
'arrow' becomes 'dart' (I've seen this in another clue).
'sent up' shows that the letters should be reversed in order.
'over monarch' becomes 'er' (abbreviation for Elizabeth Regina, British Queen. I am not sure about the 'over' bit.).
'dart' reversed gives 'trad'.
'trad'+'er'='TRADER'
Can you help me to learn more?
(Other definitions for trader that I've seen before include "Tarred the dealer badly" , "Dealer, monger" , "He buys and sells goods" , "Red tar (anag)" , "Person in the business of buying and selling" .)