check-in vs check in

check-in is a noun but check in is not a noun.

Word	Noun	Adjective	Verb	Adverb
check-in	Yes	No	No	No
check in	No	No	Yes	No

check-in (noun)	check in (noun)
the act of reporting your presence (as at an airport or a hotel)

check-in (verb)	check in (verb)
	announce one's arrival, e.g. at hotels or airports