Is it ensure, insure, or assure?
large American coniferous tree, 1857, from Modern Latin tree genus name given 1847 by Austrian botanist Stephan Endlicher (1804-1849), originally to a different tree, the coast redwood, apparently in honor of Sequoya (a.k.a. George Guess, 1760-1843), Cherokee man who invented a system of writing for his people's language, whose name is from Cherokee (Iroquoian) Sikwayi, a word of unknown etymology.
Endlicher was a specialist in conifers, and he also was a philologist. But he never gave an etymology of this name and a search of his papers discovered no mention of Sequoya or the Cherokee writing system, and the connection is an assumption that some botanists have challenged, though no better candidate for a source has yet been found.
The giant sequoia was unseen by Europeans until 1833 and unknown to scientists until 1852. In May 1855, a pair of American botanists named it Taxodium giganteum, but that name was deemed inappropriate for several scientific reasons. Meanwhile, English botanist John Lindley, who had never been to California, in 1853 named it Wellingtonia in honor of the Duke of Wellington. "As high as Wellington towers above his contemporaries, as high towers this California tree above the forest surrounding it. Therefore, it shall bear for all time to come the name Wellingtonia gigantea." This sat poorly with the Americans, and much ink was spilled until a French botanist provided the solution by transferring Endlicher's name. In Britain still popularly called Wellingtonia.