n (North America) A deep-fried piece of dough or batter, commonly made in a toroidal or ellipsoidal shape, and mixed with various sweeteners and flavors, sometimes filled with jelly, custard or cream.
n (North America) Anything in the shape of a torus
n (North America|context|automobile) a peel-out or skid-mark in the shape of donut; a 360-degree skid.
n (North America) A spare tire, smaller than a full sized tire and is only intended for temporary use.
n A toroidal cushion typically used by hemorrhoid patients.