When you're offering something in support of an already existing thing, you're offering something auxiliary. The auxiliary police will help out the regular police with things like directing traffic and crowd control when there's a special event in town.

The Latin word auxilium means "help," and so auxiliary means something that "helps" by providing backup or support. Think of auxiliary verbs (sometimes called helper verbs), that provide support within a verb phrase, as "is" does in "Helen is playing." You can have an auxiliary engine in a car, an auxiliary cook at a restaurant, an auxiliary electrical network at a factory, or auxiliary troops standing by during battle. A "Ladies Auxiliary" functions as support for institutions such as churches, synagogues, or charities.

Definitions of auxiliary
  1. adjective
    furnishing added support
    “The mind and emotions are auxiliary to each other”
    synonyms: accessory, adjunct, adjuvant, ancillary, appurtenant
    furnishing support or assistance
  2. adjective
    functioning in a supporting capacity
    “the main library and its auxiliary branches”
    synonyms: subsidiary, supplemental, supplementary
    being of second rank or importance or value; not direct or immediate
  3. noun
    someone who acts as an assistant
    synonyms: aide
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    nurse's aide, nursing aide
    someone who assists a nurse in tasks that require little formal training
    type of:
    assistant, help, helper, supporter
    a person who contributes to the fulfillment of a need or furtherance of an effort or purpose
  4. noun
    a soldier, especially a foreign soldier, who is not part of a nation’s regular army
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    type of:
    an enlisted man or woman who serves in an army
Word Family

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