The Collaborative International Dictionary of English v.0.48:

Ruff \Ruff\, n. [Of uncertain origin: cf. Icel. r[=u]finn rough,
   uncombed, Pr. ruf rude, rough, Sp. rufo frizzed, crisp,
   curled, G. raufen to pluck, fight, rupfen to pluck, pull, E.
   rough. [root]18. Cf. Ruffle to wrinkle.]
   1. A muslin or linen collar plaited, crimped, or fluted, worn
      formerly by both sexes, now only by women and children.
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            Here to-morrow with his best ruff on. --Shak.
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            His gravity is much lessened since the late
            proclamation came out against ruffs; . . . they were
            come to that height of excess herein, that twenty
            shillings were used to be paid for starching of a
            ruff.                                 --Howell.
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   2. Something formed with plaits or flutings, like the collar
      of this name.
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            I reared this flower; . . .
            Soft on the paper ruff its leaves I spread. --Pope.
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   3. An exhibition of pride or haughtiness.
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            How many princes . . . in the ruff of all their
            glory, have been taken down from the head of a
            conquering army to the wheel of the victor's
            chariot!                              --L'Estrange.
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   4. Wanton or tumultuous procedure or conduct. [Obs.]
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            To ruffle it out in a riotous ruff.   --Latimer.
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   5. (Mil.) A low, vibrating beat of a drum, not so loud as a
      roll; a ruffle.
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   6. (Mach.) A collar on a shaft ot other piece to prevent
      endwise motion. See Illust. of Collar.
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   7. (Zool.) A set of lengthened or otherwise modified feathers
      round, or on, the neck of a bird.
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   8. (Zool.)
      (a) A limicoline bird of Europe and Asia (Pavoncella
          pugnax, syn. Philomachus pugnax) allied to the
          sandpipers. The males during the breeding season have
          a large ruff of erectile feathers, variable in their
          colors, on the neck, and yellowish naked tubercles on
          the face. They are polygamous, and are noted for their
          pugnacity in the breeding season. The female is called
          reeve, or rheeve.
      (b) A variety of the domestic pigeon, having a ruff of its
          neck.
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WordNet (r) 3.0 (2006):

Philomachus pugnax
    n 1: common Eurasian sandpiper; the male has an erectile neck
         ruff in breeding season [syn: ruff, Philomachus pugnax]