The Collaborative International Dictionary of English v.0.48:

Assistant \As*sist"ant\, a. [Cf. F. assistant, p. pr. of
   assister.]
   1. Helping; lending aid or support; auxiliary.
      [1913 Webster]

            Genius and learning . . . are mutually and greatly
            assistant to each other.              --Beattie.
      [1913 Webster]

   2. (Mil.) Of the second grade in the staff of the army; as,
      an assistant surgeon. [U.S.]
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   Note: In the English army it designates the third grade in
         any particular branch of the staff. --Farrow.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Assistant \As*sist"ant\, n.
   1. One who, or that which, assists; a helper; an auxiliary; a
      means of help.
      [1913 Webster]

            Four assistants who his labor share.  --Pope.
      [1913 Webster]

            Rhymes merely as assistants to memory. --Mrs.
                                                  Chapone.
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   2. An attendant; one who is present. --Dryden.
      [1913 Webster]

WordNet (r) 3.0 (2006):

assistant
    adj 1: of or relating to a person who is subordinate to another
           [syn: adjunct, assistant]
    n 1: a person who contributes to the fulfillment of a need or
         furtherance of an effort or purpose; "my invaluable
         assistant"; "they hired additional help to finish the work"
         [syn: assistant, helper, help, supporter]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "assistant":
   acolyte, adjutant, agent, aid, aide, aide-de-camp, aider, ancilla,
   assistant professor, associate, associate professor, attendant,
   attorney, auxiliary, benefactor, best man, co-worker, coadjutant,
   coadjutor, coadjutress, coadjutrix, deputy, emeritus, employee,
   executive officer, factor, fall guy, flunky, girl Friday, help,
   helper, helpmate, helpmeet, henchman, hired hand, hired man,
   hireling, inferior, instructor, junior, lecturer, lieutenant,
   man Friday, mercenary, minion, myrmidon, paranymph,
   paraprofessional, patsy, pensioner, professor, professor emeritus,
   proxy, reader, retired professor, right-hand man, second,
   secondary, servant, sideman, stooge, striker, subordinate,
   subsidiary, supporting actor, supporting instrumentalist, tutor,
   underling, understrapper, visiting professor, worker, workfellow,
   yokemate