English Reference
adjective · noun

auxiliary

adj. · n.
US /ɑɡˈzɪɫiɛɹi/ UK /ɔːksˈɪliəɹi/ aux·il·iary UK spelling auxiliaries

  1. 01 C1 Advanced Formal

    adj.giving extra help or support to a main person, group, or system.

    adj.providing supplementary or additional help and support to a primary entity.

    Simple

    The hospital hired auxiliary staff to help during the busy winter season.

    In context

    The main engine failed, but the auxiliary power unit kicked in immediately to keep the ship's navigation systems running.

  2. 02 C1 Advanced Technical

    adj.kept ready to use if the main thing fails or if there is an emergency.

    adj.functioning as a reserve or backup intended for use in exceptional circumstances.

    Simple

    The building has an auxiliary water tank in case the city supply stops.

    In context

    Engineers designed an auxiliary cooling system to prevent a meltdown if the primary pumps were compromised.

  3. 03 C1 Advanced Formal

    n.a person or thing that provides extra help, especially in the military or a large organization.

    n.an individual or group that acts in a supportive or subsidiary capacity, often within a military or medical hierarchy.

    Simple

    She volunteered as a nurse's auxiliary at the local clinic.

    In context

    The army relied heavily on local auxiliaries to navigate the difficult mountain terrain during the campaign.

  4. 04 B2 Upper Intermediate Technical

    n.a helping verb like 'be', 'do', or 'have' that is used with another verb.

    n.a verb used in forming the tenses, moods, and voices of other verbs.

    Simple

    In the sentence 'I am eating', the word 'am' is an auxiliary.

    In context

    The student struggled to distinguish between the primary auxiliary and the main lexical verb in complex passive constructions.

    Usage

    Common auxiliaries in English include 'be', 'do', and 'have', as well as modal verbs like 'can' and 'must'.

    helping verb
    lexical verb

Critics of the last proposal have compared the idea to the auxiliary police structures set up by the Nazis, which led to the creation of a police state.

The Guardian· 5 Sept 2026

Just when things are looking dire for John and Sarah, the T-800 reboots on auxiliary power and shoots the T-1000 with a grenade launcher.

Ars Technica· 28 Aug 2026

From Latin auxiliārius (“assistant, ally”), equiv. to auxiliāris (“helping, aiding”), from auxilium (“help, aid”), from augēre (“to increase”).

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

This entry
Origin Latin auxiliārius
Level C1 · Advanced
Frequency Frequent
Updated