Webster's English Dictionary

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cleavage

cleav.age \'kle--vij\ n 1a: the quality of a crystallized substance or rock 
   of splitting along defi nite planes 1b: a fragment (as of a diamond) 
   obtained by splitting  2: the action of cleaving : the state of being cleft 
    3: cell division; esp : the series of mitotic divisions of the egg  that 
   results in the formation of the blastomeres and changes the single-celled 
   zygote into a multicellular embryo