a series of persons relieving one another or taking turns; shift.
a fresh set of dogs or horses posted in readiness for use in a hunt, on a journey, etc.
Sports. relay race. a length or leg in a relay race.
Machinery. an automatic control device in which the settings of valves, switches, etc., are regulated by a powered element, as a motor, solenoid, or pneumatic mechanism actuated by a smaller, sensitive element.
Electricity. a device, usually consisting of an electromagnet and an armature, by which a change of current or voltage in one circuit is used to make or break a connection in another circuit or to affect the operation of other devices in the same or another circuit.