sleep tight

: the natural periodic suspension of consciousness during which the powers of the body are restored — compare REM sleep, slow-wave sleep

: a state resembling sleep: such as

: a state of torpid inactivity

: to rest in a state of sleep

: to be in a state (as of quiescence or death) resembling sleep

: to have sexual relations

: having elements close together

: so close in structure as to prevent passage or escape (as of liquid, gas, or light) — compare lightproof, watertight

: fitting very close to the body

: fast, tightly, firmly

: in a sound manner : soundly