What does auxiliary mean?
Auxiliary functions both as a noun and an adjective, and at its core carries the idea of providing help, support, or backup. As a noun, it can refer to a person who assists — such as an auxiliary nurse or volunteer — or, in grammar, to a special class of verbs like be, do, and have, which combine with main verbs to form questions, negatives, and different tenses. As an adjective, it describes anything supplementary or held in reserve, as in auxiliary power supplies or auxiliary troops. The word derives from the Latin auxilium, meaning 'help', which also gives us related terms like auxin in botany. Common across formal writing, technical contexts, and everyday speech alike, auxiliary is a versatile term that conveys dependence on something additional rather than primary. Its most frequent modern appearance may well be in discussions of grammar, where auxiliary verbs are fundamental to how English sentences are constructed.
A person or thing that provides supplementary help or support, especially one held in reserve; also, in grammar, a verb used alongside a main verb to express tense, mood, voice, or aspect.
"During the crisis, the charity relied heavily on its auxiliaries."
In grammar, common auxiliary verbs in English include be, do, have, will, shall, can, and must.
Providing additional or supplemental help; functioning as a backup or reserve rather than the primary resource.
"The spacecraft carried an auxiliary battery in case the main power failed."
Standard plural for all noun senses, whether referring to helpers, supporting forces, organizations, or grammatical verbs.
"English has more than twenty modal auxiliaries."
Every English sentence you speak likely leans on an 'auxiliary' — the little verbs like do, have, and will quietly doing the heavy grammatical lifting.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of auxiliary
Auxiliary comes from the Latin auxilium, meaning 'help' or 'aid', itself derived from the Latin verb augere, 'to increase'. It entered English in the early 17th century, initially used in military contexts to describe supporting troops. Over time its use broadened into general senses of assistance and, by the 18th century, into grammar to describe helping verbs. Cognates from the same Latin root include auxin, a plant hormone named for its growth-promoting properties.
Word family
Usage notes
In grammar, 'auxiliary' is often shortened informally to 'auxiliary' alone or paired as 'helping verb' in American English. In everyday speech outside grammar, it frequently appears attributively before nouns ('auxiliary power', 'auxiliary staff'). The plural 'auxiliaries' is standard for both people/things and the grammatical sense.
Don't confuse with
Ancillary means subordinate or additional in a supporting role, while auxiliary specifically implies providing help or backup, often as a reserve.
Accessory is a thing added to something else to enhance it, whereas auxiliary provides essential backup or support.