Source : Webster's Revised Unabridged Dictionary (1913)

Backset \Back"set`\, n. [Back, adv. + set.]
   1. A check; a relapse; a discouragement; a setback.

   2. Whatever is thrown back in its course, as water.

            Slackwater, or the backset caused by the overflow.
                                                  --Harper's
                                                  Mag.

Backset \Back"set`\, v. i.
   To plow again, in the fall; -- said of prairie land broken up
   in the spring. [Western U.S.]