We don't have synonyms for mitrailleuse yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are mitrailleur, mitraillette and mitrailleuses.
(n) :
(historical, military) A breech-loading machine gun consisting of a number of barrels fitted together, so arranged that the barrels can be fired simultaneously, or successively, and rapidly.
(n) :
(historical, military) A breech-loading machine gun consisting of a number of barrels fitted together, so arranged that the barrels can be fired simultaneously, or successively, and rapidly.