stand-by

(noun) something that can be relied on when needed. Synonyms: standby.

(noun) an actor able to replace a regular performer when required. Synonyms: understudy, standby.

(verb) not act or do anything. Synonyms: stand by. Example: "He just stood by when the police beat up the demonstrators."

(verb) be available or ready for a certain function or service. Synonyms: stand by, stick around, stick about.

(verb) be loyal to. Synonyms: stand by, stick by, stick, adhere. Examples: "She stood by her husband in times of trouble." "The friends stuck together through the war."

(adj) ready for emergency use. Synonyms: standby. Examples: "A standby generator." "A standby crew."