Yakima, one of the most extensively used geographic terms in the State of Washington, is applied to a county, city, river, valley, pass in the Cascade Range, Indian tribe and Indian reservation. As in many other cases the name was first applied to the river and the natives who occupied the land drained by the river. Lewis and Clark, 1805-1806, give the name as "Tapteal," which they spell in several ways. Elliott Coues, the scholarly editor of their journals, gives a number of synonyms, such as "Eyakama."....John H. Lynch, of Yakima, quotes the pioneer Jack Splawn as authority for "lake water" as the meaning of Yakima...Henry Gannett says the word means "black bear."...The bureau of American Ethnology says the word means "runaway" and that the native name of the tribe was "Waptailmim" meaning "people of the narrow river."....David Thompson, of the North West Company of Montreal referred to the Indians on July 8, 1811, as "Skaemena."...Alexander Ross was with the Astorians, 1811, though his book Adventures of the First Settlers on the Oregon or Columbia River was not published until 1849, in which he uses the name "Eyakema."...The Wilkes Expedition, 1841, refers to the river by the name as now spelled....In framing the treaty of June 9, 1855, Governor Isaac I. Stevens referred to the river and tribe as "Yakama."...'Yakima City was incorporated December 1, 1883. Twelve months later, when it had 400 inhabitants, the surveyors of the Northern pacific railroad laid out the town, upon a broad and liberal scale, and proposed to the people of the latter that if they would consent to be removed to the new town they should be given as many lots there as they possessed in the old, and have besides their buildings moved upon them without cost to the owners. Such an agreement in writing was signed by a majority of the citizens, and in the winter and spring of 1884-1885 over 100 buildings were moved on trucks and rollers, hotels, a bank, and other business houses doing their usual business enroute. This was a good stroke of policy on the part of the railroad, general land commissioner, and the company, as it definitely settled opposition, both to the new town and the corporation, which also received a year's growth for North Yakima in ninety days' time'....By act of the State Legislature approved January 30, 1917, and to go into effect on January 1, 1918, the city was permitted to drop the word "North" from its name. The same Legislature also changed the name of the older town of Yakima to Union Gap.
Origin of Washington Geographic Names, 1923