put something to sleep
put something to sleep1 kill (an animal, especially an old, sick, or badly injured one) painlessly. euphemistic 2 put (a computer) on standby while it is not being used.
put somebody/something to ˈsleep
1 give somebody drugs (= an anaesthetic) before an operation to make them unconscious: Before the operation we’ll put you to sleep, so don’t worry, you won’t feel a thing.
2 kill a sick or injured animal by giving it drugs so that it dies without pain: She took her old dog to the vet and he put it to sleep.