freebooter
[noun]
Synonyms: marauder, bandit, brigand, bummer, cateran, forager, looter, pillager, plunderer, raider, pirate, buccaneer, corsair, picaroon, rover, sea dog, sea robber, sea rover, sea wolf

[TahlilGaran] English Synonym Dictionary ▲

free‧boot‧er /ˈfriːbuːtə $ -ər/ noun [countable]
[Date: 1500-1600; Language: Dutch; Origin: vrijbuiter, from vrij 'free' + buit 'stolen things, booty']
someone who joins in a war in order to steal other people’s goods and money

[TahlilGaran] Dictionary of Contemporary English ▲