The Collaborative International Dictionary of English v.0.48:

Granny \Gran"ny\, n.
   A grandmother; a grandam; familiarly, an old woman.
   [1913 Webster]

   Granny's bend, or Granny's knot (Naut.), a kind of
      insecure knot or hitch; a reef knot crossed the wrong way.
      [1913 Webster]

WordNet (r) 3.0 (2006):

granny
    n 1: the mother of your father or mother [syn: grandma,
         grandmother, granny, grannie, gran, nan, nanna]
    2: an old woman
    3: a reef knot crossed the wrong way and therefore insecure
       [syn: granny knot, granny]