The Collaborative International Dictionary of English v.0.48:

Digress \Di*gress"\, n.
   Digression. [Obs.] --Fuller.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

            Moreover she beginneth to digress in latitude.
                                                  --Holland.
      [1913 Webster]

            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.
      [1913 Webster]

   2. To turn aside from the right path; to transgress; to
      offend. [R.]
      [1913 Webster]

            Thy abundant goodness shall excuse
            This deadly blot on thy digressing son. --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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: digress, stray, divagate, wander]
    2: wander from a direct or straight course [syn: sidetrack,
       depart, digress, straggle]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "digress":
   bear off, bend, branch off, bypass, change the bearing, curve,
   depart, depart from, detour, deviate, divagate, divaricate,
   diverge, drift, excurse, get sidetracked, go around, go astray,
   go round about, heel, make a detour, maunder, ramble, roam, sheer,
   shift, stray, swerve, tack, trend, turn, turn aside, vary, veer,
   wander