auxiliary

Auxiliary is an adjective meaning providing supplementary or supportive help. It comes from Latin auxilium meaning “help” and is used to describe things that assist a primary subject or function. Auxiliary services, devices, or personnel complement but are not central to the main operation. Common phrases include auxiliary staff, auxiliary power unit, and auxiliary heating in buildings or vehicles. In engineering, an auxiliary system offers backup or ancillary support to the primary equipment, often operating in parallel or during maintenance or emergencies.

As a noun, an auxiliary is a person or thing that provides assistance. It can refer to staff such as an auxiliary nurse or auxiliary police officer, or to a tool, device, or program that aids a larger workflow or system. In computing, an auxiliary program or process runs alongside a primary program to perform auxiliary tasks such as maintenance, data processing, or utilities.

In linguistics, an auxiliary (also called a helping verb) is a function word used with a main verb to express tense, aspect, mood, voice, or modality. English examples include forms of be, have, and do, and modal verbs like can, may, must. They combine with lexical verbs to form periphrastic tenses such as “have eaten” or to indicate passive voice, questions, or negation. The distinction between auxiliary and main verbs varies across languages; some rely on inflection rather than separate auxiliary words.