auxiliary

Word family

• auxiliaries
  nounC1

Synonym discussion

Sense: adjective/1

All four words describe something that helps a more important person or activity, but they sit at different levels of formality and apply to different things. 'Supporting' is the most everyday and works for both people and ideas — a supporting actor, a supporting argument. 'Auxiliary' is more formal and tends to label official roles or equipment, especially in hospitals, the military, and engineering — auxiliary nurse, auxiliary generator. 'Supplementary' stresses that something is added on top of what is already there, often for information or income — supplementary notes, a supplementary pension. 'Ancillary' is the most formal and is common in legal, business, and academic writing for services or staff that surround a main activity — ancillary services, ancillary staff. So you would say 'auxiliary nurse' in a hospital report, 'supporting actor' on a film poster, 'supplementary reading' on a course handout, and 'ancillary services' in a business contract.

Common collocations

Etymology

The word reached English in the early 1600s from Latin 'auxiliarius', meaning 'giving help', built on 'auxilium' ('help, aid'). It first appeared in military writing for foreign troops who fought alongside the Roman or English regular army. From there it spread to general supporting roles, then to backup equipment in the industrial age, and finally to the grammar term for helping verbs that linguists adopted in the nineteenth century.