From Longman Dictionary of Contemporary Englishfreebooterfree‧boot‧er /ˈfriːbuːtə $ -ər/ noun [countable] SCCsomeone who joins in a war in order to steal other people’s goods and money
Examples from the Corpus
freebooter• I object to you pacing round this house shouting at our servants like some freebooter.Origin freebooter (1500-1600) Dutch vrijbuiter, from vrij “free” + buit “stolen things, booty” 