Auxiliary means giving extra support, or helping the main one. An auxiliary engine, auxiliary power, the auxiliary services.
In grammar an auxiliary verb is one that helps another carry tense or mood: be, have and do, plus the modals. In the forces and in hospitals it names support staff, and an auxiliary power unit is the small engine that runs an aircraft on the ground.
1adjectiveauxiliaryGiving extra support, or helping the main one.
“The hospital switched to an auxiliary generator when the power went out.”
auxiliary is a quality of support.
Latin auxiliarius comes from auxilium, help, from augere, to increase. Augment is a relative.
Proto-Indo-European
*h₂ewg-
Latin
auxiliārius — assistant, ally
English, today
auxiliary
Built from
From Latin auxiliārius (“assistant, ally”), equiv. to auxiliāris (“helping, aiding”), from auxilium (“help, aid”), from augēre (“to increase”).
Etymology from Wiktionary, CC BY-SA