We don't have synonyms for sapper yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are supper, snapper and dapper.
(n) :
one who saps; specifically, one who is employed in working at saps, building and repairing fortifications, and the like. Often known as a combat engineer or military engineer; (British colloquial) an officer or private of the Royal Engineers
(n) :
one who saps; specifically, one who is employed in working at saps, building and repairing fortifications, and the like. Often known as a combat engineer or military engineer; (British colloquial) an officer or private of the Royal Engineers