standby

stand·by  (stndb)

n. pl. stand·bys

1. One that can always be relied on, as in an emergency.

2. A favorite or frequent choice.

3. One kept in readiness to serve as a substitute.

adj.

1. Kept in reserve for use when needed: a standby generator.

2. Of, relating to, or waiting for unreserved travel space that is made available by an airline only shortly before departure: standby passengers.

adv.

On a standby basis: flew standby to New York.

Idiom:

on standby

Ready and waiting.

Thesaurus

Noun	1.	standby - something that can be relied on when needed thing - an artifact; "how does this thing work?"
	2.	standby - an actor able to replace a regular performer when required understudy actor, histrion, thespian, role player, player - a theatrical performer
Adj.	1.	standby - ready for emergency use; "a standby generator"; "a standby crew" secondary - being of second rank or importance or value; not direct or immediate; "the stone will be hauled to a secondary crusher"; "a secondary source"; "a secondary issue"; "secondary streams"