n. A hybrid created by grafting a tomato plant onto the roots of a tobacco plant.
An Oregon scientist who enjoyed a Simpsons' cartoon episode about Homer crossing a tomato plant with tobacco managed to match the feat, reports said Thursday.

Rob Baur told Portland's KPTV the episode prompted him to create a real "tomacco" plant by grafting a tomato plant onto tobacco roots.
—“Homer Simpson inspires plant inventor,” United Press International, November 13, 2003
Rob Baur of Lake Oswego, Oregon, dreamed of bringing to life his favorite The Simpsons episode, one from 1999 in which Homer grows "tomacco," a combination tomato-tobacco plant. Even though it tastes foul and has a brown, gooey center, the entire town becomes addicted to the fruit after one bite, and Homer gets rich.

Baur grafted a tomato plant onto tobacco roots, and voilà, he had a real, live tomacco plant. The two plants can successfully become one because they come from the same plant family, which also includes eggplant and the deadly nightshade. The tomacco even bore fruit, although Baur said he believes it's poisonous because it likely contains a lethal amount of nicotine.
—Kristen Philipkoski, “Simpsons Plant Seeds of Invention,” Wired News, November 07, 2003
1999 (earliest)
Homer begins challenging everyone around him to duels after he sees a Zorro film at the Googoplex. Most people back down, until Homer meets an old-fashioned Colonel who takes him up on his dare. Unable to get out of the contest with the Colonel, Homer and his family flee to the country, where they become farmers. Farm life is difficult until Homer creates a new crop called tomacco—tomatoes crossed with tobacco. The new fruit is disgusting to eat, but incredibly addictive. Selling barrel upon barrel of tomacco, Homer attracts the attention of some tobacco industry executives who want to capitalize on his new crop. Will Homer sell his cash crop for a pile of cash? Why are all the animals who ate tomacco suddenly going berserk? Would it really have been so bad to duel that Colonel after all?
—“E-I-E-I-(Annoyed Grunt),” The Simpsons Episode Guide, November 07, 1999