Reading the article is interesting: Sushi's only consistent ingredient is rice - since it can be made with fish, octopus, vegetables, fruits or eggs - and it's all sushi. However, the origins of sushi come from pickling excess fish with fermenting rice, which would preserve the fish. The rice was discarded and the resulting fish was called sushi (literally translates to "sour tasting") - so despite rice being the important part of the dish, the word comes from a pickled fish.

(for those too lazy to read it: that picked fish was eaten for hundreds of years before, in the 16-800s, it started to be served pressed into a mound of rice. It wasn't until the 1820s that the pickled fish was replaced with fresh fish and the nigirizushi we know today was born courtesy of chef Hanaya Yohei.)