auxiliary

Adjective

• furnishing added support
  • an ancillary pump
    
  • an adjuvant discipline to forms of mysticism
    
  • The mind and emotions are auxiliary to each other
    

• functioning in a supporting capacity
  • the main library and its auxiliary branches
    

Noun

• someone who acts as assistant

Related words

• Synonyms: 
  accessory , adjunct , ancillary , adjuvant , appurtenant , subsidiary , supplemental , supplementary , aide