Ship on move suddenly reversed (6)
I believe the answer is:
trader
'ship' is the definition.
(trading ship)
'on move suddenly reversed' is the wordplay.
'on' becomes 're' (regarding).
'move suddenly' becomes 'd'art' (I've seen this in another clue).
'reversed' shows that the letters should be reversed in order.
're'+'dart'='redart'
'redart' reversed gives 'TRADER'.
(Other definitions for trader that I've seen before include "Merchant ship; dealer" , "Tarred the dealer badly" , "Tarred like merchant" , "One buys and sells" , "One in business" .)