(computing) the state of a computer system in which the drives and interfaces are switched off, and the only task running is monitoring external activity, particularly a key press which restores the system to its active state from the random access memory.

Someone who sleeps. / That which lies dormant, as a law. / A spy, saboteur, or terrorist who lives unobtrusively in a community until activated by a prearranged signal; may be part of a sleeper cell.

(rare) To mark a calf by cutting its ear.

(rail transport, Britain) A railroad tie. / (carpentry) A structural beam in a floor running perpendicular to both the joists beneath and floorboards above.

(idiomatic) Hidden, in reserve.

(pathology) Brief interruptions of breathing during sleep.

Characterized by an absence of sleep.

(idiomatic) To leave things as they are; especially, to avoid restarting or rekindling an old argument; to leave disagreements in the past.

(transitive) To cause (someone) to sleep. / (transitive) To help (someone) to bed; put to bed. / (transitive, figuratively) To render dormant.

(informal) A sleepy person. / The ruddy duck.