The Collaborative International Dictionary of English v.0.48:

centriole \centriole\ n. (Biol.)
   one of two small cylindrical cell organelles composes of nine
   triplet microtubules, which form the asters during mitosis.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

centriole
    n 1: one of a pair of small cylindrical cell organelles near the
         nucleus in animal cells; composed of nine triplet
         microtubules and form the asters during mitosis