additional; supplementary; reserve

an auxiliary police force.

used as a substitute or reserve in case of need

The hospital has an auxiliary power system in case of a blackout.

(of a boat) having an engine that can be used to supplement the sails

an auxiliary yawl.

giving support; serving as an aid; helpful

The mind and emotions are auxiliary to each other. Passion is auxiliary to art.

a person or thing that gives aid of any kind; helper.

an organization allied with, but subsidiary to, a main body of restricted membership, esp. one composed of members' relatives

The men's club and the ladies' auxiliary were merged into one organization.

auxiliary verb.

auxiliaries, foreign troops in the service of a nation at war.

Navy . a naval vessel designed for other than combat purposes, as a tug, supply ship, or transport.

Nautical . a sailing vessel carrying an auxiliary propulsion engine or engines.

adjective

body , main

adjective

abetting , accessory , adjuvant , ancillary , appurtenant , backup , complementary , contributory , extra , reserve , secondary , spare , subordinate , subservient , subsidiary , supporting , assistant , collateral , supportive , emergency , standby , supplemental , supplementary , adminicular , syncategorematic

noun

accessory , accomplice , adjutant , ally , assistant , associate , companion , confederate , crutch , partner , reserve , subordinate , supporter , aide , coadjutant , coadjutor , deputy , helper , lieutenant , second , additional , adjunct , adjunctive , adminicle , ancillary , appendix , backup , branch , emergency , help , incidental , satellite , secondary , spare , subsidiary , supplement , supporting , tributary