The Collaborative International Dictionary of English v.0.48:

Ombre \Om"bre\, n. [F., of uncertain origin.] (Zool.)
   A large Mediterranean food fish (Umbrina cirrhosa): --
   called also umbra, and umbrine.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Penumbra \Pe*num"bra\, n. [NL., fr. L. paene almost + umbra
   shade.]
   1. An incomplete or partial shadow.
      [1913 Webster]

   2. (Astron.) The shadow cast, in an eclipse, where the light
      is partly, but not wholly, cut off by the intervening
      body; the space of partial illumination between the umbra,
      or perfect shadow, on all sides, and the full light. --Sir
      I. Newton.
      [1913 Webster]

   Note: The faint shade surrounding the dark central portion of
         a solar spot is also called the penumbra, and
         sometimes umbra.
         [1913 Webster]

   3. (Paint.) The part of a picture where the shade
      imperceptibly blends with the light.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Umbra \Um"bra\, n.; pl. Umbrae. [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.
          [1913 Webster]

   2. (Zool.) Any one of several species of sciaenoid food
      fishes of the genus Umbrina, especially the
      Mediterranean species (Umbrina cirrhosa), which is
      highly esteemed as a market fish; -- called also ombre,
      and umbrine.
      [1913 Webster]

   Umbra tree (Bot.), a tree (Phytolacca dioica) 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).
      [1913 Webster]

WordNet (r) 3.0 (2006):

umbra
    n 1: a region of complete shadow resulting from total
         obstruction of light

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "umbra":
   adumbration, dark shade, eidolon, ghost, gloom, haunt, mere shadow,
   penumbra, phantasm, phantom, revenant, shade, shadiness, shadow,
   shadows numberless, silhouette, skiagram, skiagraph, spook,
   umbrage, umbrageousness