let in

US /lɛt ɪn/
UK /lɛt ɪn/
"let in" picture
1.

to allow someone or something to enter a place

:
Could you please let the cat in?
The bouncer wouldn't let him in because he was underage.
2.

to reveal a secret or allow someone to know something private

:
She accidentally let in on her plans for the surprise party.
Don't let anyone in on our secret.