hold in

verb3

1. •
   To keep something to oneself; to prevent from escaping.

   • When the world is a monster bad to swallow you whole, kick the clay that holds those teeth in, throw your trolls out the door. — 1985
2. •
   (old-fashioned) To restrain oneself.

   • He wanted to laugh and could hardly hold in.
3. •
   To keep (someone) in prison or jail.