The Collaborative International Dictionary of English v.0.48:

Muffin \Muf"fin\, n. [From Muff.]
   A light, spongy, cylindrical cake, used for breakfast and
   tea.
   [1913 Webster]

WordNet (r) 3.0 (2006):

muffin
    n 1: a sweet quick bread baked in a cup-shaped pan [syn:
         muffin, gem]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "muffin":
   Danish, Danish pastry, English muffin, Parker House roll,
   Yorkshire pudding, bagel, bialy, bialystoker, bun,
   clover-leaf roll, coffee cake, crescent roll, croissant, cross bun,
   crumpet, gem, hard roll, hot cross bun, kaiser roll, onion roll,
   pinwheel roll, popover, roll, scone, soft roll