I. stand ‧ by 1 BrE AmE , ˈstand-by /ˈstændbaɪ/ noun ( plural standbys )
1 . on standby
a) ready to help immediately if you are needed:
A special team of police were kept on standby.
b) if you are on standby to do something, for example to travel by plane, you are on a list of people who may be allowed to do it if places become available:
We can put you on standby.
⇨ ↑ stand by (4)
2 . [countable] something that is kept ready so that it can be used when needed:
Powdered milk is a good standby in an emergency.
II. standby 2 BrE AmE adjective [only before noun]
a standby ticket is one that you can get only if places become available, for example if other people cannot use their tickets