Source : Webster's Revised Unabridged Dictionary (1913)

Astride \A*stride"\, adv. [Pref. a- + stride.]
   With one leg on each side, as a man when on horseback; with
   the legs stretched wide apart; astraddle.

         Placed astride upon the bars of the palisade. --Sir W.
                                                  Scott.

         Glasses with horn bows sat astride on his nose.
                                                  --Longfellow.

Source : WordNet®

astride
     adv 1: with one leg on each side; "she sat astride the chair" [syn:
             {astraddle}]
     2: with the legs stretched far apart