trench mortar vs high-angle gun

trench mortar and high-angle gun both are nouns.

Word	Noun	Adjective	Verb	Adverb
trench mortar	Yes	No	No	No
high-angle gun	Yes	No	No	No

As nouns, high-angle gun is a hypernym of trench mortar; that is, high-angle gun is a word with a broader meaning than trench mortar:

trench mortar: a muzzle-loading high-angle gun with a short barrel that fires shells at high elevations for a short range
high-angle gun: a cannon that can be fired at a high elevation for relatively short ranges

trench mortar (noun)	high-angle gun (noun)
a muzzle-loading high-angle gun with a short barrel that fires shells at high elevations for a short range	a cannon that can be fired at a high elevation for relatively short ranges