The doughnut wasn’t always called a nut, and when it was first called a nut, the name actually made sense.
First of all, let’s dismiss one spurious but widespread legend reported by otherwise reputable sources:
that the name was invented during World War I because the fighting “doughboys” went “nuts” over the doughnuts and coffee that were routinely distributed to soldiers by the Red Cross.
Actually the name goes much further back, to a time before doughnuts had holes.
Washington Irving described in his Knickerbocker’s History of New York in 1809 “an enormous dish of balls of sweetened dough, fried in hog’s fat, and called doughnuts or olykoeks.”
In the late 15th century, Dutch bakers originated olykoeks (“oil cakes”), a ball named for the amount of grease absorbed in the deep-frying process.
When the Pilgrims left England in the early 1600s and took refuge in the Netherlands, they learned the secrets of making olykoeks.
Before the little group of religious fanatics left for America on the Mayflower, they gave the cakes a new name, dough nuts, because the little balls looked like walnuts.
So, ironically, little round “doughnut holes” aren’t anything new, they’ve simply gone back to the original format.