Take off in boat over region (8)
I believe the answer is:
subtract
'take off' is the definition.
(synonyms)
'boat over region' is the wordplay.
'boat' becomes 'sub' (I've seen this before).
'over' is a charade indicator (letters next to each other).
'region' becomes 'tract' (both can mean a large piece of land).
'sub'+'tract'='SUBTRACT'
'in' acts as a link.
(Other definitions for subtract that I've seen before include "Knock off" , "Deduct" , "Take one quantity away from another" , "Withdraw" , "Remove" .)