› [U, no plural] the state you are in when you are sleeping, or a period of time when you are sleeping: I haven't had a good night's sleep (= a long sleep at night) for weeks. You need to go home and get some sleep. It took me ages to get to sleep (= to succeed in sleeping). He died peacefully in his sleep.
go to sleep › to begin to sleep: Babies often go to sleep after a feed. › informal If part of your body goes to sleep, you cannot feel it: I'd been sitting on my feet and they'd gone to sleep.
put sth to sleep › to kill an animal that is very old or ill
could do sth in your sleep › to be able to do something very easily