STANDBY

I. noun (plural ~s) Date: 1796 1. one to be relied on especially in emergencies, a favorite or reliable choice or resource, one that is held in reserve ready for use ; substitute , II. adjective Date: 1872 held near at hand and ready for use , relating to the act or condition of standing by , of, relating to, or traveling by an airline service in which the passenger must wait for an available unreserved seat , III. adverb Date: 1971 on a ~ basis