Source : Webster's Revised Unabridged Dictionary (1913)

Adjuvant \Ad"ju*vant\, a. [L. adjuvans, p. pr. of adjuvare to
   aid: cf. F. adjuvant. See {Aid}.]
   Helping; helpful; assisting. [R.] ``Adjuvant causes.''
   --Howell.

Adjuvant \Ad"ju*vant\, n.
   1. An assistant. [R.] --Yelverton.

   2. (Med.) An ingredient, in a prescription, which aids or
      modifies the action of the principal ingredient.

Source : WordNet®

adjuvant
     adj 1: 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}, {ancillary},
             {appurtenant}, {auxiliary}, {subsidiary}]
     2: enhancing the action of a medical treatment; "the adjuvant
        action of certain bacteria"
     n : an additive that enhances the effectiveness of medical
         treatment