More on the etymology ...
From Take Our Word for It:
The earliest occurrence of the word is in the work of Washington Irving (1809). He had to define the word, so we can assume that it was not a widely known dish at the time, at least to his audience. And, interestingly, he defines doughnuts as "balls of sweetened dough, fried in hog's fat". This suggests that doughnuts were not named after knots or nuts and bolts, but instead after nuts like walnuts or pecans. They were balls of dough that, when fried to a deep golden brown, resembled nuts. Doughnuts only took their torus shape to overcome a problem inherent in balls of dough - uncooked centers. Removing the centers ensured that the doughnuts would be cooked throughout.
Similarly, from The Origin of Things:
Now for the origin of the word. In the early 1600s, the Pilgrims learned how to make olykoeks and gave them a new name...doughnuts. The new name came about because the little balls of dough looked like walnuts.
