Auxiliary
/ɔːkˈsɪli.əɹi/
noun
A person or group that acts in an auxiliary manner.
A sailing vessel equipped with an engine.
(grammar) An auxiliary verb.
adjective
Helping; giving assistance or support.
“auxiliary troops”
Supplementary or subsidiary.
Held in reserve for exceptional circumstances.
Synonyms: motorsailer, accessory, accessory, ancillary