Source : Webster's Revised Unabridged Dictionary (1913)

Doughnut \Dough"nut\, n.
   A small cake (usually sweetened) fried in a kettle of boiling
   lard.

Source : WordNet®

doughnut
     n 1: a toroidal shape; "a ring of ships in the harbor"; "a halo
          of smoke" [syn: {ring}, {halo}, {annulus}, {anulus}, {anchor
          ring}]
     2: a small ring-shaped friedcake [syn: {donut}, {sinker}]