The Collaborative International Dictionary of English v.0.48:

Therewith \There*with"\, adv.
   1. With that or this. "I have learned in whatsoever state I
      am, therewith to be content." --Phil. iv. 11.
      [1913 Webster]

   2. In addition; besides; moreover.
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            To speak of strength and therewith hardiness.
                                                  --Chaucer.
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   3. At the same time; forthwith. [Obs.] --Johnson.
      [1913 Webster]

WordNet (r) 3.0 (2006):

therewith
    adv 1: with that or this or it; "I have learned that whatever
           state I am, therewith to be content"- Phil.4:11