army engineer vs sapper

army engineer and sapper both are nouns.

Word	Noun	Adjective	Verb	Adverb
army engineer	Yes	No	No	No
sapper	Yes	No	No	No

As nouns, sapper is a hyponym of army engineer; that is, sapper is a word with a more specific, narrower meaning than army engineer:

army engineer: a member of the military who is trained in engineering and construction work
sapper: a military engineer who does sapping (digging trenches or undermining fortifications)

army engineer (noun)	sapper (noun)
a member of the military who is trained in engineering and construction work	a military engineer who does sapping (digging trenches or undermining fortifications)