piranha vs moss-trooper

piranha and moss-trooper both are nouns.

Word	Noun	Adjective	Verb	Adverb
piranha	Yes	No	No	No
moss-trooper	Yes	No	No	No

As nouns, moss-trooper is a hyponym of piranha; that is, moss-trooper is a word with a more specific, narrower meaning than piranha:

piranha: someone who attacks in search of booty
moss-trooper: a marauder and plunderer (originally operating in the bogs between England and Scotland)

piranha (noun)	moss-trooper (noun)
small voraciously carnivorous freshwater fishes of South America that attack and destroy living animals	a marauder and plunderer (originally operating in the bogs between England and Scotland)
someone who attacks in search of booty