A sapper is a soldier who works to dig tunnels or to do other building work for the army.
Sappers are very important for the army because they help make things safe and help the army move around.
Examples:
The sapper dug a tunnel for the army.
The sapper helped build a bridge.
Sappers are very good at building things.
The sapper's job is to dig and build.
The sapper can dig a tunnel in one day.
The sapper's work is very important for the army.