A seat, on an aircraft etc, that can be reclined to form a bed. / (US) A small compartment on a long-distance truck in which the driver can sleep when taking a break.

plural of dark sleeper

Odontobutis obscura, a freshwater goby found in East Asia

(rail transport, chiefly UK) A railroad tie.

plural of sleeper cell

A truck or lorry cab with a bunk behind the seating area, in which the driver can sleep during rest breaks on long journeys away from home.

plural of sleeper agent

A spy who is placed in a target country or organisation, not to undertake an immediate mission, but rather to act as a potential asset if activated.

plural of rough sleeper

(idiomatic, euphemistic) A homeless person who sleeps outdoors.