Webster's Revised Unabridged Dictionary · 1913

check in

check in (chek`in") , intransitive verb

To register as a guest at a hotel, inn, motel. etc. Converse of check out.

check-in (chek"in) , noun

The act of registering as a guest at a hotel, inn, motel. etc; the act of checking in. Used also attributively, as the check-in counter at a hotel.