sapper vs military engineer

sapper and military engineer both are nouns.

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

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

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

Other hypernyms of sapper include army engineer.

sapper (noun)	military 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