1.
When you ~ or ~to a hotel or clinic, or if someone checks you in, you arrive and go through the necessary procedures before you stay there.
I’ll ring the hotel. I’ll tell them we’ll ~ tomorrow...
He has checked into an alcohol treatment centre...
Check us in at the hotel and wait for my call.
= register
? check out
PHRASAL VERB: V P, V P n, V n P
2.
When you ~ at an airport, you arrive and show your ticket before going on a flight.
He had checked in at Amsterdam’s Schiphol airport for a flight to Manchester.
PHRASAL VERB: V P
see also check-in , check 6