engine vs bolt thrower

engine and bolt thrower both are nouns.

Word	Noun	Adjective	Verb	Adverb
engine	Yes	No	No	No
bolt thrower	Yes	No	No	No

As nouns, bolt thrower is a hyponym of engine; that is, bolt thrower is a word with a more specific, narrower meaning than engine:

engine: an instrument or machine that is used in warfare, such as a battering ram, catapult, artillery piece, etc.
bolt thrower: ancient missile weapon that throws bolts or stones

Other hyponyms of engine include battering ram, catapult, ballista.

engine (noun)	bolt thrower (noun)
motor that converts thermal energy to mechanical work	ancient missile weapon that throws bolts or stones
a wheeled vehicle consisting of a self-propelled engine that is used to draw trains along railway tracks
an instrument or machine that is used in warfare, such as a battering ram, catapult, artillery piece, etc.
something used to achieve a purpose