We don't have synonyms for matross yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are matrass, matress and matrons.
(n) :
(military, now historical) An artilleryman next in rank to a gunner; a gunner's mate, especially one who assists the gunners in loading, firing, and sponging the guns.
(n) :
(military, now historical) An artilleryman next in rank to a gunner; a gunner's mate, especially one who assists the gunners in loading, firing, and sponging the guns.