Auxiliary (adjective)

1. Providing additional help, support, or resources.
2. Serving as a secondary or supplementary feature.
3. Serving as backup in case of emergency.

Origin:

Late 16th century: from latin auxiliaris, from auxilium 'help', from augere 'to increase'.

Examples:

1. The army has several auxiliary units that provide support to the main force.
2. This generator serves as an auxiliary power source in case of an electricity outage.
3. Auxiliary staff is being hired to cope with the increasing workload in the office.
4. Auxiliary services, such as daycare and transportation, are essential for working parents.
5. The auxiliary library, which has been set up in a nearby school, is a great resource for students.