The Collaborative International Dictionary of English v.0.48:

Clown \Clown\, v. i.
   To act as a clown; -- with it. [Obs.]
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         Beshrew me, he clowns it properly indeed. --B. Jonson.
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The Collaborative International Dictionary of English v.0.48:

Clown \Clown\ (kloun), n. [Cf. Icel. klunni a clumsy, boorish
   fellow, North Fries. kl["o]nne clown, dial. Sw. klunn log,
   Dan. klunt log, block, and E. clump, n.]
   1. A man of coarse nature and manners; an awkward fellow; an
      ill-bred person; a boor. --Sir P. Sidney.
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   2. One who works upon the soil; a rustic; a churl.
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            The clown, the child of nature, without guile.
                                                  --Cowper.
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   3. The fool or buffoon in a play, circus, etc.
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            The clown shall make those laugh whose lungs are
            tickle o'the sere.                    --Shak.
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WordNet (r) 3.0 (2006):

clown
    n 1: a rude or vulgar fool [syn: clown, buffoon]
    2: a person who amuses others by ridiculous behavior [syn:
       clown, buffoon, goof, goofball, merry andrew]
    v 1: act as or like a clown [syn: clown, clown around,
         antic]