The Collaborative International Dictionary of English v.0.48:

Spicule \Spic"ule\, n. [L. spiculum a little point, a dart.]
   1. A minute, slender granule, or point.
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   2. (Bot.) Same as Spicula.
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   3. (Zool.) Any small calcareous or siliceous body found in
      the tissues of various invertebrate animals, especially in
      sponges and in most Alcyonaria.
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   Note: Spicules vary exceedingly in size and shape, and some
         of those found in siliceous sponges are very complex in
         structure and elegant in form. They are of great use in
         classification.
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               Description of the Illustration:
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               a Acerate; b Tricurvate, or Bowshaped; c d
               Hamate; e Broomshaped; f Scepterellate; g
               Spinispirulate; h Inequi-anchorate; i Sexradiate;
               j A Trichite Sheaf; k Six-rayed Capitate; l
               Rosette of Esperia; m Equi-anchorate.
         [1913 Webster]

WordNet (r) 3.0 (2006):

spicule
    n 1: small pointed structure serving as a skeletal element in
         various marine and freshwater invertebrates e.g. sponges
         and corals [syn: spicule, spiculum]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "spicule":
   bramble, brier, bristle, burr, cactus, catchweed, cleavers,
   goose grass, needle, nettle, pine needle, prickle, quill, spiculum,
   spike, spikelet, spine, sticker, thistle, thorn, yucca