Source : Webster's Revised Unabridged Dictionary (1913)

Redan \Re*dan"\ (r?*d?n"), n. [F., for OF. redent a double
   notching or jagging, as in the teeth of a saw, fr. L. pref.
   re- re- + dens, dentis, a tooth. Cf. {Redented}.] [Written
   sometimes {redent} and {redens}.]
   1. (Fort.) A work having two parapets whose faces unite so as
      to form a salient angle toward the enemy.

   2. A step or vertical offset in a wall on uneven ground, to
      keep the parts level.