Source : Webster's Revised Unabridged Dictionary (1913)

Umbra \Um"bra\, n.; pl. {Umbr[ae]}. [L., a shadow.]
   1. (Astron.)
      (a) The conical shadow projected from a planet or
          satellite, on the side opposite to the sun, within
          which a spectator could see no portion of the sun's
          disk; -- used in contradistinction from penumbra. See
          {Penumbra}.
      (b) The central dark portion, or nucleus, of a sun spot.
      (c) The fainter part of a sun spot; -- now more commonly
          called penumbra.

   2. (Zo["o]l.) Any one of several species of sci[ae]noid food
      fishes of the genus {Umbrina}, especially the
      Mediterranean species ({U. cirrhosa}), which is highly
      esteemed as a market fish; -- called also {ombre}, and
      {umbrine}.

   {Umbra tree} (Bot.), a tree ({Phytolacca diocia}) of the same
      genus as pokeweed. It is native of South America, but is
      now grown in southern Europe. It has large dark leaves,
      and a somber aspect. The juice of its berries is used for
      coloring wine. --J. Smith (Dict. Econ. Plants).

Source : WordNet®

umbra
     n : a region of complete shadow resulting from total obstruction
         of light
     [also: {umbrae} (pl)]

umbrae
     See {umbra}