Sewellel \Se*wel"lel\, n. [Of American Indian origin.] (Zo["o]l.) A peculiar gregarious burrowing rodent ({Haplodon rufus}), native of the coast region of the Northwestern United States. It somewhat resembles a muskrat or marmot, but has only a rudimentary tail. Its head is broad, its eyes are small and its fur is brownish above, gray beneath. It constitutes the family {Haplodontid[ae]}. Called also {boomer}, {showt'l}, and {mountain beaver}.