petard vs explosive device

petard and explosive device both are nouns.

Word	Noun	Adjective	Verb	Adverb
petard	Yes	No	No	No
explosive device	Yes	No	No	No

As nouns, explosive device is a hypernym of petard; that is, explosive device is a word with a broader meaning than petard:

petard: an explosive device used to break down a gate or wall
explosive device: device that bursts with sudden violence from internal energy

petard (noun)	explosive device (noun)
an explosive device used to break down a gate or wall	device that bursts with sudden violence from internal energy