kissing bug vs assassin bug

kissing bug and assassin bug both are nouns.

Word	Noun	Adjective	Verb	Adverb
kissing bug	Yes	No	No	No
assassin bug	Yes	No	No	No

As nouns, assassin bug is a hypernym of kissing bug; that is, assassin bug is a word with a broader meaning than kissing bug:

kissing bug: large bloodsucking bug
assassin bug: a true bug: long-legged predacious bug living mostly on other insects; a few suck blood of mammals

Other hypernyms of kissing bug include reduviid.

kissing bug (noun)	assassin bug (noun)
large bloodsucking bug	a true bug: long-legged predacious bug living mostly on other insects; a few suck blood of mammals