flatten vs steamroller

flatten is not a noun while steamroller is a noun.

Word	Noun	Adjective	Verb	Adverb
flatten	No	No	Yes	No
steamroller	Yes	No	Yes	No

As verbs, steamroller is a hyponym of flatten; that is, steamroller is a word with a more specific, narrower meaning than flatten:

Other hyponyms of flatten include steamroll, splat, roll, roll out, laminate.

flatten (noun)	steamroller (noun)
	vehicle equipped with heavy wide smooth rollers for compacting roads and pavements
	a massive inexorable force that seems to crush everything in its way

flatten (verb)	steamroller (verb)
become flat or flatter	make level or flat with a steamroller
make flat or flatter	overwhelm by using great force
lower the pitch of (musical notes)	crush with a steamroller as if to level
	proceed with great force
	bring to a specified state by overwhelming force or pressure