Policeman in charge on board tender (7)
I believe the answer is:
officer
'policeman' is the definition.
('officer' can be a synonym of 'policeman')
'in charge on board tender' is the wordplay.
'in charge' becomes 'ic'.
'on board' means one lot of letters goes inside another.
'tender' becomes 'offer' ('offer' can be a synonym of 'tender').
'ic' inserted inside 'offer' is 'OFFICER'.
(Other definitions for officer that I've seen before include "In the army, he's commissioned" , "Policeman (or other authority)" , "Person holding a commission in the services" , "Possibly a major" , "Major, say" .)