auxiliary

(noun) someone who acts as assistant. Synonyms: aide.

(adj) functioning in a supporting capacity. Synonyms: subsidiary, supplemental, supplementary. Example: "The main library and its auxiliary branches."

(adj) furnishing added support. Synonyms: accessory, adjunct, ancillary, adjuvant, appurtenant. Examples: "An ancillary pump." "An adjuvant discipline to forms of mysticism." "The mind and emotions are auxiliary to each other."