Source : Webster's Revised Unabridged Dictionary (1913)

Digress \Di*gress"\, v. i. [imp. & p. p. {Digressed}; p. pr. &
   vb. n. {Digressing}.] [L. digressus, p. p. of digredi to go
   apart, to deviate; di- = dis- + gradi to step, walk. See
   {Grade}.]
   1. To step or turn aside; to deviate; to swerve; especially,
      to turn aside from the main subject of attention, or
      course of argument, in writing or speaking.

            Moreover she beginneth to digress in latitude.
                                                  --Holland.

            In the pursuit of an argument there is hardly room
            to digress into a particular definition as often as
            a man varies the signification of any term. --Locke.

   2. To turn aside from the right path; to transgress; to
      offend. [R.]

            Thy abundant goodness shall excuse This deadly blot
            on thy digressing son.                --Shak.

Digress \Di*gress"\, n.
   Digression. [Obs.] --Fuller.

Source : WordNet®

digress
     v 1: lose clarity or turn aside especially from the main subject
          of attention or course of argument in writing, thinking,
          or speaking; "She always digresses when telling a
          story"; "her mind wanders"; "Don't digress when you give
          a lecture" [syn: {stray}, {divagate}, {wander}]
     2: wander from a direct or straight course [syn: {sidetrack}, {depart},
         {straggle}]