look out vs lookout

look out is not a noun while lookout is a noun.

Word	Noun	Adjective	Verb	Adverb
look out	No	No	Yes	No
lookout	Yes	No	No	No

look out (noun)	lookout (noun)
	the act of looking out
	a structure commanding a wide view of its surroundings
	an elevated post affording a wide view
	a person employed to keep watch for some anticipated event

look out (verb)	lookout (verb)
to protect someone's interests
be vigilant, be on the lookout or be careful