Source : Webster's Revised Unabridged Dictionary (1913)

Betwixt \Be*twixt"\, prep. [OE. betwix, bitwix, rarely bitwixt,
   AS. betweox, betweohs, betweoh, betw[=i]h; pref. be- by + a
   form fr. AS. tw[=a] two. See {Between}.]
   1. In the space which separates; between.

            From betwixt two aged oaks.           --Milton.

   2. From one to another of; mutually affecting.

            There was some speech of marriage Betwixt myself and
            her.                                  --Shak.

   {Betwixt and between}, in a midway position; so-so; neither
      one thing nor the other. [Colloq.]

Source : WordNet®

betwixt
     adv : in the interval; "dancing all the dances with little rest
           between" [syn: {between}]