auxiliary

nouns

someone who acts as assistant
aide, auxiliary

adjectives

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