WordNet sense 1 (a period of time spent sleeping):

nap

WordNet sense 2 (a torpid state resembling deep sleep):

sopor

WordNet sense 3 (a natural and periodic state of rest during which consciousness of the world is suspended):

slumber

WordNet sense 4 (euphemisms for death (based on an analogy between lying in a bed and in a tomb)):

quietus, rest, eternal rest, eternal sleep

WordNet sense 5 (be asleep):

kip, catch some Z's, log Z's