loaf sugar

noun (esp formerly)
  1. a large conical mass of hard refined sugar; sugar loaf
  2. small cube-shaped lumps of this, the form in which it was often sold
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Examples from the Web for loaf sugar

Historical Examples of loaf sugar