Freebooter, n.
Etymology: [D. vrijbuiter, fr. vrijbuiten to plunder; vrij free + buit booty, akin to E. booty. See Free, and Booty, and cf. Filibuster.]
One who plunders or pillages without the authority of national warfare; a member of a predatory band; a pillager; a buccaneer; a sea robber. Bacon.
Shades of meaning
Fernald has no entry of its own for freebooter; he lists it under robber.
He lists it without comment; the entries above explain its neighbors.