The Collaborative International Dictionary of English v.0.48:

Sewellel \Se*wel"lel\, n. [Of American Indian origin.] (Zool.)
   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 Haplodontidae. Called also boomer, showt'l, and
   mountain beaver.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mountain \Moun"tain\ (moun"t[i^]n), a.
   1. Of or pertaining to a mountain or mountains; growing or
      living on a mountain; found on or peculiar to mountains;
      among mountains; as, a mountain torrent; mountain pines;
      mountain goats; mountain air; mountain howitzer.
      [1913 Webster]

   2. Like a mountain; mountainous; vast; very great.
      [1913 Webster]

            The high, the mountain majesty of worth. --Byron.
      [1913 Webster]

   Mountain antelope (Zool.), the goral.

   Mountain ash (Bot.), an ornamental tree, the Pyrus
      Americana (or Sorbus Americana), producing beautiful
      bunches of red berries. Its leaves are pinnate, and its
      flowers white, growing in fragrant clusters. The European
      species is the Pyrus aucuparia, or rowan tree.

   Mountain barometer, a portable barometer, adapted for safe
      transportation, used in measuring the heights of
      mountains.

   Mountain beaver (Zool.), the sewellel.

   Mountain blue (Min.), blue carbonate of copper; azurite.

   Mountain cat (Zool.), the catamount. See Catamount.

   Mountain chain, a series of contiguous mountain ranges,
      generally in parallel or consecutive lines or curves.

   Mountain cock (Zool.), capercailzie. See Capercailzie.

   Mountain cork (Min.), a variety of asbestus, resembling
      cork in its texture.

   Mountain crystal. See under Crystal.

   Mountain damson (Bot.), a large tree of the genus
      Simaruba (Simaruba amarga) growing in the West Indies,
      which affords a bitter tonic and astringent, sometimes
      used in medicine.

   Mountain dew, Scotch whisky, so called because often
      illicitly distilled among the mountains. [Humorous]

   Mountain ebony (Bot.), a small leguminous tree (Bauhinia
      variegata) of the East and West Indies; -- so called
      because of its dark wood. The bark is used medicinally and
      in tanning.

   Mountain flax (Min.), a variety of asbestus, having very
      fine fibers; amianthus. See Amianthus.

   Mountain fringe (Bot.), climbing fumitory. See under
      Fumitory.

   Mountain goat. (Zool.) See Mazama.

   Mountain green. (Min.)
      (a) Green malachite, or carbonate of copper.
      (b) See Green earth, under Green, a.

   Mountain holly (Bot.), a branching shrub (Nemopanthes
      Canadensis), having smooth oblong leaves and red berries.
      It is found in the Northern United States.

   Mountain laurel (Bot.), an American shrub (Kalmia
      latifolia) with glossy evergreen leaves and showy
      clusters of rose-colored or white flowers. The foliage is
      poisonous. Called also American laurel, ivy bush, and
      calico bush. See Kalmia.

   Mountain leather (Min.), a variety of asbestus, resembling
      leather in its texture.

   Mountain licorice (Bot.), a plant of the genus Trifolium
      (Trifolium Alpinum).

   Mountain limestone (Geol.), a series of marine limestone
      strata below the coal measures, and above the old red
      standstone of Great Britain. See Chart of Geology.

   Mountain linnet (Zool.), the twite.

   Mountain magpie. (Zool.)
      (a) The yaffle, or green woodpecker.
      (b) The European gray shrike.

   Mountain mahogany (Bot.) See under Mahogany.

   Mountain meal (Min.), a light powdery variety of calcite,
      occurring as an efflorescence.

   Mountain milk (Min.), a soft spongy variety of carbonate of
      lime.

   Mountain mint. (Bot.) See Mint.

   Mountain ousel (Zool.), the ring ousel; -- called also
      mountain thrush and mountain colley. See Ousel.

   Mountain pride, or Mountain green (Bot.), a tree of
      Jamaica (Spathelia simplex), which has an unbranched
      palmlike stem, and a terminal cluster of large, pinnate
      leaves.

   Mountain quail (Zool.), the plumed partridge (Oreortyx
      pictus) of California. It has two long, slender,
      plumelike feathers on the head. The throat and sides are
      chestnut; the belly is brown with transverse bars of black
      and white; the neck and breast are dark gray.

   Mountain range, a series of mountains closely related in
      position and direction.

   Mountain rice. (Bot.)
      (a) An upland variety of rice, grown without irrigation,
          in some parts of Asia, Europe, and the United States.
      (b) An American genus of grasses (Oryzopsis).

   Mountain rose (Bot.), a species of rose with solitary
      flowers, growing in the mountains of Europe (Rosa
      alpina).

   Mountain soap (Min.), a soft earthy mineral, of a brownish
      color, used in crayon painting; saxonite.

   Mountain sorrel (Bot.), a low perennial plant (Oxyria
      digyna with rounded kidney-form leaves, and small
      greenish flowers, found in the White Mountains of New
      Hampshire, and in high northern latitudes. --Gray.

   Mountain sparrow (Zool.), the European tree sparrow.

   Mountain spinach. (Bot.) See Orach.

   Mountain tobacco (Bot.), a composite plant (Arnica
      montana) of Europe; called also leopard's bane.

   Mountain witch (Zool.), a ground pigeon of Jamaica, of the
      genus Geotrygon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mountain beaver
    n 1: bulky nocturnal burrowing rodent of uplands of the Pacific
         coast of North America; the most primitive living rodent
         [syn: mountain beaver, sewellel, Aplodontia rufa]