Definition of turn in phrasal verb from the Oxford Advanced American Dictionary

 

turn in

 phrasal verb
phrasal verb
 
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Phrasal Verbs
  1. 1to face or curve toward the center Her feet turn in.
  2. 2(old-fashioned) to go to bed It's late—I think I'll turn in.

turn somebodyin

(informal)
 
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to take someone to the police or someone in authority because they have committed a crime She threatened to turn him in to the police. He decided to turn himself in.

    turn somethingin

     
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  1. 1to give back something that you no longer need You must turn in your pass when you leave the building.
  2. 2 to give something to someone in authority They turned in a petition with 80,000 signatures. I haven't even turned in Monday's work yet.
  3. 3to achieve a score, performance, profit, etc. The champion turned in a superb performance to retain her title.
See the Oxford Advanced Learner's Dictionary entry: turn in