A standby is something (or someone) you can rely on in an emergency, like the bicycle you keep as a standby in case your old car won't start.

In basketball, the players on the bench are the standbys for their teammates on the court; and in theater, an actor's understudy is her standby. When something is "on standby," it's ready to jump in or be used immediately. And when you fly on standby, you are ready to take an extra seat on a flight if one becomes available. Standby comes from nautical slang for "a vessel kept for emergencies," originally "that which stands by one."

Definitions of standby

n something that can be relied on when needed

Type of:
an artifact

n an actor able to replace a regular performer when required

Type of:
actor, histrion, player, role player, thespian
a theatrical performer

adj ready for emergency use

“a standby generator”
“a standby crew”
being of second rank or importance or value; not direct or immediate

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