What is the meaning of auxiliary?

noun

• Someone who acts as assistant.
  • synonyms: aide

adjective

• Functioning in a supporting capacity.
  • usage: "the main library and its auxiliary branches"
  • synonyms: subsidiary, supplemental, supplementary
• Furnishing added support.
  • usage: "an ancillary pump"; "an adjuvant discipline to forms of mysticism"; "The mind and emotions are auxiliary to each other"
  • synonyms: accessory, adjunct, ancillary, adjuvant, appurtenant