1. Lowest rank in the Royal Engineers. Equivalent to Private, Craftsman, Gunner etc.
2. One who digs a 'Sap'. Early military engineering involved methods of attacking besieged castles. One method was to dig a tunnel or 'Sap' under the walls to make them collapse. If detected the besieged would dig a counter-sap with the intention of intercepting the incoming tunnellers. Likely to lead to either vicious Hand to Hand Combat (imagine 20 blokes fighting in an air conditioning vent - a tradition continued today in the local sticky carpet by modern sappers) or being buried alive when one side collapses the others tunnel.
- Any member of the Royal Engineers. From the lowest Sapper to the CRE, regardless of rank, is proud to be called a Sapper.