The Collaborative International Dictionary of English v.0.48:

Digressive \Di*gress"ive\, a. [Cf. F. digressif.]
   Departing from the main subject; partaking of the nature of
   digression. --Johnson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

digressive
    adj 1: of superficial relevance if any; "a digressive allusion
           to the day of the week"; "a tangential remark" [syn:
           digressive, tangential]
    2: (of e.g. speech and writing) tending to depart from the main
       point or cover a wide range of subjects; "amusingly
       digressive with satirical thrusts at women's fashions among
       other things"; "a rambling discursive book"; "his excursive
       remarks"; "a rambling speech about this and that" [syn:
       digressive, discursive, excursive, rambling]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "digressive":
   O-shaped, aberrant, aberrative, aimless, ambagious, backhand,
   backhanded, by the way, circuitous, circular, deflectional,
   departing, desultory, deviant, deviating, deviative, deviatory,
   devious, discursive, divagational, divergent, episodic, errant,
   erratic, excursive, helical, indirect, labyrinthine, left-handed,
   loose, maundering, mazy, meandering, oblique, orbital,
   out-of-the-way, planetary, rambling, rotary, round, roundabout,
   roving, serpentine, shifting, side, sidelong, sinister, sinistral,
   snaky, spiral, stray, swerving, turning, twisting, undirected,
   vagrant, veering, wandering, winding, zigzag