put to sleep

Short definition from Wiktionary

Verb

1. 1
   To cause (someone) to sleep.
2. 2
   To help (someone) to bed; put to bed.
3. 3
   To render dormant.
4. 4
   To kill an animal painlessly, often with an injection; to euthanize.
5. 5
   To give a general anesthetic prior to surgery.