sleep, slumber -- (a natural and periodic state of rest during which consciousness of the world is suspended; "he didn't get enough sleep last night"; "calm as a child in dreamless slumber")
sleep, sopor -- (a torpid state resembling deep sleep)
sleep, nap -- (a period of time spent sleeping; "he felt better after a little sleep"; "there wasn't time for a nap")
rest, eternal rest, sleep, eternal sleep, quietus -- (euphemisms for death (based on an analogy between lying in a bed and in a tomb); "she was laid to rest beside her husband"; "they had to put their family pet to sleep")