The Collaborative International Dictionary of English v.0.48:

Looming \Loom"ing\, n.
   The indistinct and magnified appearance of objects seen in
   particular states of the atmosphere. See Mirage.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Loom \Loom\ (l[=oo]m), v. i. [imp. & p. p. Loomed (l[=oo]md);
   p. pr. & vb. n. Looming.] [OE. lumen to shine, Icel. ljoma;
   akin to AS. le['i]ma light, and E. light; or cf. OF. lumer to
   shine, L. luminare to illumine, lumen light; akin to E.
   light. [root]122. See Light not dark.]
   1. To appear above the surface either of sea or land, or to
      appear enlarged, or distorted and indistinct, as a distant
      object, a ship at sea, or a mountain, esp. from
      atmospheric influences; as, the ship looms large; the land
      looms high.
      [1913 Webster]

            Awful she looms, the terror of the main. --H. J.
                                                  Pye.
      [1913 Webster]

   2. To rise and to be eminent; to be elevated or ennobled, in
      a moral sense.
      [1913 Webster]

            On no occasion does he [Paul] loom so high, and
            shine so gloriously, as in the context. --J. M.
                                                  Mason.
      [1913 Webster]

   3. To become imminent; to impend.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Mirage \Mi`rage"\, n. [F., fr. mirer to look at carefully, to
   aim, se mirer to look at one's self in a glass, to reflect,
   to be reflected, LL. mirare to look at. See Mirror.]
   An optical effect, sometimes seen on the ocean, but more
   frequently in deserts, due to total reflection of light at
   the surface common to two strata of air differently heated.
   The reflected image is seen, commonly in an inverted
   position, while the real object may or may not be in sight.
   When the surface is horizontal, and below the eye, the
   appearance is that of a sheet of water in which the object is
   seen reflected; when the reflecting surface is above the eye,
   the image is seen projected against the sky. The fata
   Morgana and looming are species of mirage.
   [1913 Webster]

         By the mirage uplifted the land floats vague in the
         ether,
         Ships and the shadows of ships hang in the motionless
         air.                                     --Longfellow.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "looming":
   about to be, already in sight, approaching, at hand, brewing,
   close, close at hand, coming, fata morgana, forthcoming, future,
   gathering, going to happen, immediate, imminent, impendent,
   impending, in danger imminent, in prospect, in reserve, in store,
   in the cards, in the offing, in the wind, in view, instant,
   lowering, lurking, menacing, mirage, near, near at hand, nearing,
   on the horizon, overhanging, preparing, that will be, threatening,
   to come, upcoming, waiting