sapper vs army engineer

sapper and army engineer both are nouns.

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

As nouns, army engineer is a hypernym of sapper; that is, army engineer is a word with a broader meaning than sapper:

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

Other hypernyms of sapper include military engineer.

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