Source : Webster's Revised Unabridged Dictionary (1913)

Ancillary \An"cil*la*ry\, a. [L. ancillaris, fr. ancilla a
   female servant.]
   Subservient or subordinate, like a handmaid; auxiliary.

         The Convocation of York seems to have been always
         considered as inferior, and even ancillary, to the
         greater province.                        --Hallam.

Source : WordNet®

ancillary
     adj : relating to something that is added but is not essential;
           "an ancillary pump"; "an adjuvant discipline to forms
           of mysticism"; "The mind and emotions are auxilliary to
           each other" [syn: {accessory}, {adjunct}, {adjuvant}, {appurtenant},
            {auxiliary}, {subsidiary}]