The Collaborative International Dictionary of English v.0.48:

Discursion \Dis*cur"sion\, n. [LL. discursio a running different
   ways. See Discourse.]
   The act of discoursing or reasoning; range, as from thought
   to thought. --Coleridge.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "discursion":
   Wanderjahr, aberrancy, aberration, afoot and lighthearted, aside,
   bend, bias, branching off, bumming, bypath, byway, circuitousness,
   corner, crook, curve, declination, departure, detour, deviance,
   deviancy, deviation, deviousness, digression, divagation,
   divarication, divergence, diversion, dogleg, double, drift,
   drifting, episode, errantry, excursion, excursus, exorbitation,
   flitting, gadding, hairpin, hoboism, indirection, itineracy,
   itinerancy, nomadism, obliquity, parenthesis, peregrination,
   pererration, ramble, rambling, roam, roaming, rove, roving, sheer,
   shift, shifting, shifting course, shifting path, side path,
   side road, sidetrack, skew, slant, straying, sweep, swerve,
   swerving, swinging, tack, traipsing, turn, turning, twist,
   vagabondage, vagabondia, vagabondism, vagrancy, variation, veer,
   wandering, wayfaring, yaw, zigzag