The Collaborative International Dictionary of English v.0.48:

Joke \Joke\, n. [L. jocus. Cf Jeopardy, Jocular, Juggler.]
   [1913 Webster]
   1. Something said for the sake of exciting a laugh; something
      witty or sportive (commonly indicating more of hilarity or
      humor than jest); a jest; a witticism; as, to crack
      good-natured jokes.
      [1913 Webster]

            And gentle dullness ever loves a joke. --Pope.
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            Or witty joke our airy senses moves
            To pleasant laughter.                 --Gay.
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   2. Something not said seriously, or not actually meant;
      something done in sport.
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            Inclose whole downs in walls, 't is all a joke.
                                                  --Pope.
      [1913 Webster]

   In joke, in jest; sportively; not meant seriously.

   Practical joke. See under Practical.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Practical \Prac"ti*cal\, a. [L. practicus active, Gr. ? fit for
   doing or performing, practical, active, fr. ? to do, work,
   effect: cf. F. pratique, formerly also practique. Cf.
   Pragmatic, Practice.]
   1. Of or pertaining to practice or action.
      [1913 Webster]

   2. Capable of being turned to use or account; useful, in
      distinction from ideal or theoretical; as, practical
      chemistry. "Man's practical understanding." --South. "For
      all practical purposes." --Macaulay.
      [1913 Webster]

   3. Evincing practice or skill; capable of applying knowledge
      to some useful end; as, a practical man; a practical mind.
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   4. Derived from practice; as, practical skill.
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   Practical joke, a joke put in practice; a joke the fun of
      which consists in something done, in distinction from
      something said; esp., a trick played upon a person.
      [1913 Webster]

WordNet (r) 3.0 (2006):

practical joke
    n 1: a prank or trick played on a person (especially one
         intended to make the victim appear foolish)