The Collaborative International Dictionary of English v.0.48:

Excursion \Ex*cur"sion\ [L. excursio: cf. F. excursion. See
   Excurrent.]
   1. A running or going out or forth; an expedition; a sally.
      [1913 Webster]

            Far on excursion toward the gates of hell. --Milton.
      [1913 Webster]

            They would make excursions and waste the country.
                                                  --Holland.
      [1913 Webster]

   2. A journey chiefly for recreation; a pleasure trip; a brief
      tour; as, an excursion into the country.
      [1913 Webster]

   3. A wandering from a subject; digression.
      [1913 Webster]

            I am not in a scribbling mood, and shall therefore
            make no excursions.                   --Cowper.
      [1913 Webster]

   4. (Mach.) Length of stroke, as of a piston; stroke. [An
      awkward use of the word.]

   Syn: Journey; tour; ramble; jaunt. See Journey.
        [1913 Webster]

WordNet (r) 3.0 (2006):

excursion
    n 1: a journey taken for pleasure; "many summer excursions to
         the shore"; "it was merely a pleasure trip"; "after
         cautious sashays into the field" [syn: excursion,
         jaunt, outing, junket, pleasure trip, expedition,
         sashay]
    2: wandering from the main path of a journey [syn: digression,
       excursion]

Moby Thesaurus II by Grady Ward, 1.0:

139 Moby Thesaurus words for "excursion":
   aberrancy, aberration, airing, ambages, aside, bend, bias,
   branching off, bypass, bypath, byway, campaign, circling, circuit,
   circuition, circuitousness, circuitry, circularity, circulation,
   circumambience, circumambiency, circumambulation, circumbendibus,
   circumflexion, circumlocution, circummigration, circumnavigation,
   corner, course, crook, crosswiseness, cruise, curve, declination,
   deflection, deflexure, departure, detour, deviance, deviancy,
   deviation, deviousness, diagonality, digression, discursion,
   divagation, divarication, divergence, diversion, dogleg, double,
   drift, drifting, drive, episode, errantry, excursus, exorbitation,
   expedition, grand tour, gyre, gyring, hairpin, hike, indirection,
   indirectness, jaunt, journey, junket, lionism, meandering,
   nonconformity, obliqueness, obliquity, orbit, orbiting, outing,
   package tour, parenthesis, peregrination, pererration, pilgrimage,
   pleasure trip, progress, ramble, rambling, ride, round trip,
   roundabout, roundabout way, roundaboutness, rounding,
   rubberneck tour, run, safari, sail, sally, sheer, shift, shifting,
   shifting course, shifting path, shoot, side path, side road,
   sidetrack, sight-seeing, skew, skewness, slant, spiral, spiraling,
   squint, stalk, straying, stroll, sweep, swerve, swerving, swinging,
   tack, tour, transverseness, trek, trip, turn, turning, twist,
   vagary, variation, veer, voyage, walk, walkabout, wandering, warp,
   wheeling, yaw, zigzag