Source : Webster's Revised Unabridged Dictionary (1913)

Grandfather \Grand"fa"ther\, n.
   A father's or mother's father; an ancestor in the next degree
   above the father or mother in lineal ascent.

   {Grandfather longlegs}. (Zo["o]l.) See {Daddy longlegs}.

Source : WordNet®

grandfather
     n : the father of your father or mother [syn: {gramps}, {granddad},
          {grandad}, {granddaddy}, {grandpa}]