The Collaborative International Dictionary of English v.0.48:

Prominent \Prom"i*nent\, a. [L. prominens, -entis, p. pr. of
   prominere to jut out, to project; pro before, forward +
   minere (in comp.) to jut, project: cf. F. prominent. See
   Imminent, Eminent.]
   [1913 Webster]
   1. Standing out, or projecting, beyond the line surface of
      something; jutting; protuberant; in high relief; as, a
      prominent figure on a vase.
      [1913 Webster]

   2. Hence; Distinctly manifest; likely to attract attention
      from its size or position; conspicuous; as, a prominent
      feature of the face; a prominent building.
      [1913 Webster]

   3. Eminent; distinguished above others; as, a prominent
      character.
      [1913 Webster]

   Prominent' moth (Zool.), any moth of the family
      Notodontid[ae]; a notodontian; -- so called because the
      larva has a hump or prominence on its back. Several of the
      species are injurious to fruit trees.
      [1913 Webster]

WordNet (r) 3.0 (2006):

prominent
    adj 1: having a quality that thrusts itself into attention; "an
           outstanding fact of our time is that nations poisoned by
           anti semitism proved less fortunate in regard to their
           own freedom"; "a new theory is the most prominent feature
           of the book"; "salient traits"; "a spectacular rise in
           prices"; "a striking thing about Picadilly Circus is the
           statue of Eros in the center"; "a striking resemblance
           between parent and child" [syn: outstanding,
           prominent, salient, spectacular, striking]
    2: conspicuous in position or importance; "a big figure in the
       movement"; "big man on campus"; "he's very large in financial
       circles"; "a prominent citizen" [syn: big, large,
       prominent]

Moby Thesaurus II by Grady Ward, 1.0:

189 Moby Thesaurus words for "prominent":
   Olympian, absolute, acclaimed, aerial, airy, altitudinous,
   apparent, arrant, arresting, ascendant, ascending, aspiring,
   august, authoritarian, authoritative, authorized, autocratic,
   blatant, bold, bulging, celebrated, chief, clean-cut, clear,
   clear as crystal, clear-cut, clothed with authority, colossal,
   commanding, competent, consequential, considerable, conspicuous,
   controlling, creditable, crystal-clear, defined, definite,
   discernible, distinct, distinguishable, distinguished, dominant,
   dominating, duly constituted, egregious, elevated, eminent,
   emissile, empowered, esteemed, estimable, ethereal, evident,
   ex officio, exalted, exceptional, excrescent, excrescential,
   extraordinary, extruding, eye-catching, famed, famous, first,
   flagrant, foremost, glaring, glorious, godlike, governing, great,
   hanging out, haughty, hegemonic, hegemonistic, heroic, high,
   high-pitched, high-reaching, high-set, high-up, honorable, honored,
   identifiable, illustrious, imperative, important, in focus,
   in relief, in the foreground, in the limelight, influential,
   jutting, lauded, leading, lofty, magnanimous, magnificent, main,
   majestic, marked, memorable, mighty, momentous, monocratic,
   monumental, mounting, noble, notable, noted, noteworthy,
   noticeable, notorious, obtrusive, obvious, of mark, official,
   ostensible, outstanding, outtopping, overlooking, overtopping,
   patent, plain, popular, potent, powerful, preeminent, prestigious,
   principal, prognathous, projecting, pronounced, protrudent,
   protruding, protrusile, protrusive, protuberant, protuberating,
   puissant, raised, ranking, rare, recognizable, remarkable,
   rememberable, renowned, reputable, respected, ruling, salient,
   senior, signal, significant, soaring, special, spiring, staring,
   stark-staring, steep, sticking out, striking, sublime, substantial,
   superb, superior, superlative, supernal, supreme, telling,
   to the front, topless, toplofty, topping, totalitarian, towering,
   towery, unforgettable, unmistakable, uplifted, upreared, weighty,
   well-defined, well-known, well-marked, well-pronounced,
   well-resolved, well-thought-of