privateer

n. sailor or officer of a warship; warship, ship commissioned by a government to fight enemies

A privateer was a private warship authorized by a country's government by letters of marque to attack foreign shipping. Strictly, a privateer was only entitled to attack enemy vessels during wartime. However, states often encouraged attacks on opposing powers while at peace, or on neutral vessels during time of war, blurring the line between privateering and piracy.
See more at Wikipedia.org...

Noun
1. an officer or crew member of a privateer
(synonym) privateersman
(hypernym) officer, ship's officer
(hyponym) Hawkins, Hawkyns, Sir John Hawkins, Sir John Hawkyns
2. a privately owned warship commissioned to prey on the commercial shipping or warships of an enemy nation
(hypernym) warship, war vessel, combat ship

(v. i.)
To cruise in a privateer.
  

(n.)
The commander of a privateer.
  

(n.)
An armed private vessel which bears the commission of the sovereign power to cruise against the enemy. See Letters of marque, under Marque.
  

A vessel owned by one or by a society of private individuals, armed and equipped at his or their expense, for the purpose of carrying on a maritime war by the authority of one of the belligerent parties.

For the purpose of encouraging the owners of private armed vessels, they are usually allowed to appropriate to themselves the property they capture, or at least a large proportion of it.
   

This entry contains material from Bouvier's Legal Dictionary, a work published in the 1850's.