The Collaborative International Dictionary of English v.0.48:

Episode \Ep"i*sode\, n. [Gr. ? a coming in besides, ? episode; ?
   into, besides + ? a coming in, ? into + ? way, cf. Skr. sad
   to go: cf. F. ['e]pisode.] (Rhet.)
   A separate incident, story, or action, introduced for the
   purpose of giving a greater variety to the events related; an
   incidental narrative, or digression, separable from the main
   subject, but naturally arising from it.
   [1913 Webster]

WordNet (r) 3.0 (2006):

episode
    n 1: a happening that is distinctive in a series of related
         events
    2: a brief section of a literary or dramatic work that forms
       part of a connected series
    3: a part of a broadcast serial [syn: episode, installment,
       instalment]
    4: film consisting of a succession of related shots that develop
       a given subject in a movie [syn: sequence, episode]

Moby Thesaurus II by Grady Ward, 1.0:

114 Moby Thesaurus words for "episode":
   action, adventure, affair, anagnorisis, angle, architectonics,
   architecture, argument, aside, atmosphere, background,
   broken thread, brokenness, bypath, byway, catastrophe, chapter,
   characterization, circumstance, color, complication, continuity,
   contrivance, denouement, departure, design, development, deviation,
   device, digression, disconnectedness, disconnection,
   discontinuance, discontinuation, discontinuity, discontinuousness,
   discreteness, discursion, disjunction, event, excursion, excursus,
   experience, fable, fact, falling action, fitfulness, gimmick, go,
   hap, happening, happenstance, incident, incoherence,
   incompleteness, infix, injection, insert, insertion, insinuation,
   intercalation, interjection, interlineation, interlocution,
   intermittence, interpolation, introduction, irregularity, line,
   local color, matter, matter of fact, mood, motif, movement, mythos,
   non sequitur, noncontinuance, nonlinearity, nonseriality,
   nonuniformity, obiter dictum, occasion, occurrence, parenthesis,
   part, particular, peripeteia, phenomenon, plan, plot, reality,
   recognition, remark, rising action, scene, scheme, secondary plot,
   side path, side remark, slant, story, structure, subject, subplot,
   switch, thematic development, theme, thing, tone, topic,
   tossing-in, turn of events, twist