standby (Adjective) — Ready for emergency use. ex. "a standby generator" ex. "a standby crew"
standby (Noun) — Something that can be relied on when needed.
standby (Noun) — An actor able to replace a regular performer when required.
standby (Verb) — Not act or do anything. ex. "He just stood by when the police beat up the demonstrators"
standby (Verb) — Be available or ready for a certain function or service.
standby (Verb) — Be loyal to. ex. "She stood by her husband in times of trouble"