If you look it up in the dictionary, you’ll see the traditional “doughnut” spelling instead of the shorter version with fewer letters. Dunkin’ is actually largely responsible for popularizing the “donut” spelling, probably because “donut” is much easier to fit into a logo.

As for which spelling is the “right” one, well, you’re going to get a different answer from almost every person you ask. This is in line with the “is a hot dog a sandwich” debate. We’re going to keep having these arguments until the end of time, but no one will ever win. Unless we debate while eating donuts. Then everyone wins.