means a free rover (Dutch, buiten, to rove, whence vrijbuiter; German, freibeuter, etc ) "His forces consisted mostly of base people and freebooters " - Bacon Freeholds Estates which owe no duty or service to any lord but the sovereign (See Copyhold )
"One who goes about in search of plunder; esp a pirate or piratical adventurer " (Oxford English dictionary at the Electronic Text Center of the University of Virginia)
One who plunders or pillages without the authority of national warfare; a member of a predatory band; a pillager; a buccaneer; a sea robber