The Collaborative International Dictionary of English v.0.48:

cytoskeleton \cy`to*skel"e*ton\
   (s[imac]`t[-o]*sk[e^]l"[i^]*t'n), n. (Cell Biology)
   An arrangement of microtubules, microfilaments, and larger
   filaments within a cell serving to provide structural support
   of components of the cell, and to transport components from
   one part of the cell to another; the filaments are composed
   of protein and form a latticelike arrangement which may
   change rapidly with time.
   [PJC]

WordNet (r) 3.0 (2006):

cytoskeleton
    n 1: a microscopic network of actin filaments and microtubules
         in the cytoplasm of many living cells that gives the cell
         shape and coherence