The Collaborative International Dictionary of English v.0.48:

Loaf \Loaf\, n.; pl. Loaves. [OE. lof, laf, AS. hl[=a]f; akin
   to G. laib, OHG. hleip, Icel. hleifr, Goth. hlaifs, Russ.
   khlieb', Lith. kl["e]pas. Cf. Lady, Lammas, Lord.]
   Any thick lump, mass, or cake; especially, a large regularly
   shaped or molded mass, as of bread, sugar, or cake. --Bacon.
   [1913 Webster]

   Loaf sugar, refined sugar that has been formed into a
      conical loaf in a mold.
      [1913 Webster]

WordNet (r) 3.0 (2006):

loaf sugar
    n 1: a large conical loaf of concentrated refined sugar [syn:
         sugarloaf, sugar loaf, loaf sugar]