Real Dictionary

turn in
phrasal verb: If you turn someone in, you take them to the police or tell the police where they are because they are suspected of committing a crime. If you turn yourself in, you go to the police because you have been involved in a crime.
phrasal verb: When you turn in a completed piece of work, especially written work, you give it to the person who asked you to do it.
phrasal verb: When you turn in, you go to bed.

turn in in American English
to hand in; submit
to make a turn into; enter

turn in in British English
to go to bed for the night