1.
When you turn in , you go to bed. ( INFORMAL )
Would you like some tea before you turn in?
PHRASAL VERB : V P
2.
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.
He has been given until noon today to turn himself in to authorities...
There would be strong incentives to turn someone in...
I might today hesitate to turn in a burglar.
PHRASAL VERB : V n P to n , V n P , V P n (not pron) , also V P n (not pron) to n
3.
When you turn in a completed piece of work, especially written work, you give it to the person who asked you to do it.
Now we wait for them to turn in their essays...
I want everybody to turn a report in.
= hand in
PHRASAL VERB : V P n (not pron) , V n P
4.
If you turn something in , you return it to the place or person you borrowed it from. ( mainly AM )
I went back to the station-house to turn in my badge and gun...
= return
PHRASAL VERB : V P n (not pron)