'Sapper' definitions:

Definition of 'sapper'

From: WordNet
noun
A military engineer who lays or detects and disarms mines
noun
A military engineer who does sapping (digging trenches or undermining fortifications)

Definition of 'Sapper'

From: GCIDE
  • Sapper \Sap"per\, n. [Cf. F. sapeur.] One who saps; specifically (Mil.), one who is employed in working at saps, building and repairing fortifications, and the like. [1913 Webster]