standby

1 standby /ˈstændˌbaɪ/ noun
plural standbys /ˈstændˌbaɪz/
1 standby
/ˈstændˌbaɪ/
noun
plural standbys /ˈstændˌbaɪz/
Britannica Dictionary definition of STANDBY
[count]
: a person or thing that is available especially in emergencies
— see also stand by at 1stand

on standby

1 
: ready or available for immediate action or use
2 
: ready to travel if a ticket becomes available
2 standby /ˈstændˌbaɪ/ adjective
2 standby
/ˈstændˌbaɪ/
adjective
Britannica Dictionary definition of STANDBY
always used before a noun
: relating to or traveling by an airline service in which the passenger must wait for an available seat — see also stand by at 1stand