settle down vs roost

settle down is not a noun while roost is a noun.

Word	Noun	Adjective	Verb	Adverb
settle down	No	No	Yes	No
roost	Yes	No	Yes	No

As verbs, roost is a hyponym of settle down; that is, roost is a word with a more specific, narrower meaning than settle down:

settle down: become settled or established and stable in one's residence or life style
roost: settle down or stay, as if on a roost

settle down (noun)	roost (noun)
	a perch on which domestic fowl rest or sleep
	a shelter with perches for fowl or other birds

settle down (verb)	roost (verb)
become settled or established and stable in one's residence or life style	settle down or stay, as if on a roost
become quiet or calm, especially after a state of agitation	sit, as on a branch
settle into a position, usually on a surface or ground