Source : Webster's Revised Unabridged Dictionary (1913)

Backstitch \Back"stitch`\, n. [Back, adv. + stitch.]
   A stitch made by setting the needle back of the end of the
   last stitch, and bringing it out in front of the end.

Backstitch \Back"stitch`\, v. i.
   To sew with backstitches; as, to backstitch a seam.

Source : WordNet®

backstitch
     n : overlapping stitch made by starting next stitch at middle of
         preceding one
     v : do backstitches