WordNet (r) 3.0 (2006):

sharpener
    n 1: any implement that is used to make something (an edge or a
         point) sharper; "a knife sharpener"

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "sharpener":
   ax, blade, cold steel, cutlery, cutter, dagger, edge tools, emery,
   file, grindstone, hone, knife, naked steel, novaculite, oilstone,
   pigsticker, point, puncturer, rubstone, steel, strap, strop, sword,
   toad sticker, whetrock, whetstone, whittle