standby

or stand-by

[ stand-bahy ]
/ ˈstændˌbaɪ /

noun, plural stand·bys.

a staunch supporter or adherent; one who can be relied upon.
something upon which one can rely and therefore choose or use regularly.
something or someone held ready to serve as a substitute, especially a radio or television program used as a filler in case of cancellation of a regularly scheduled program.
a traveler who is waiting for last-minute accommodations to become available on a plane, train, or other transport as a result of a cancellation.

adjective

Idioms for standby

    on standby, in a state of readiness to act, respond, or be used immediately when needed.

Origin of standby

First recorded in 1790–1800; noun, adj. use of verb phrase stand by

Idioms and Phrases with on standby

on standby

Ready and waiting, as in We've got three more painters on standby. This expression originated in the navy in the 1940s, where it referred to someone being ready to come on duty as soon as required. From about 1960 it began to be widely used in aviation for a passenger waiting to take the first available seat on a full flight.