The Collaborative International Dictionary of English v.0.48:

Dominant \Dom"i*nant\, a. [L. dominans, -antis, p. pr. of
   dominari: cf. F. dominant. See Dominate.]
   Ruling; governing; prevailing; controlling; predominant; as,
   the dominant party, church, spirit, power.
   [1913 Webster]

         The member of a dominant race is, in his dealings with
         the subject race, seldom indeed fraudulent, . . . but
         imperious, insolent, and cruel.          --Macaulay.
   [1913 Webster]

   Dominant estate or Dominant tenement (Law), the estate to
      which a servitude or easement is due from another estate,
      the estate over which the servitude extends being called
      the servient estate or tenement. --Bouvier. --Wharton's
      Law Dict.

   Dominant owner (Law), one who owns lands on which there is
      an easement owned by another.
      [1913 Webster]

   Syn: Governing; ruling; controlling; prevailing; predominant;
        ascendant.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Dominant \Dom"i*nant\, n. (Mus.)
   The fifth tone of the scale; thus G is the dominant of C, A
   of D, and so on.
   [1913 Webster]

   Dominant chord (Mus.), the chord based upon the dominant.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dominant
    adj 1: exercising influence or control; "television plays a
           dominant role in molding public opinion"; "the dominant
           partner in the marriage" [ant: low-level,
           subordinate]
    2: (of genes) producing the same phenotype whether its allele is
       identical or dissimilar [ant: recessive]
    3: most frequent or common; "prevailing winds" [syn:
       prevailing, prevalent, predominant, dominant, rife]
    n 1: (music) the fifth note of the diatonic scale
    2: an allele that produces the same phenotype whether its paired
       allele is identical or different [syn: dominant allele,
       dominant]

Moby Thesaurus II by Grady Ward, 1.0:

181 Moby Thesaurus words for "dominant":
   absolute, accidental, all-absorbing, arch, ascendant, assertive,
   at the head, authoritarian, authoritative, authorized, autocratic,
   average, banner, besetting, boss, breve, capital, cardinal,
   central, champion, chief, clothed with authority, cock, commanding,
   common, competent, conquering, consequential, considerable,
   controlling, crotchet, crowning, current, defeating,
   demisemiquaver, dominant note, double whole note, duly constituted,
   eighth note, eminent, empowered, enharmonic, enharmonic note,
   epidemic, ex officio, first, flat, flushed with success, focal,
   foremost, general, governing, great, half note, head, headmost,
   hegemonic, hegemonistic, hemidemisemiquaver, highest, imperative,
   important, in ascendancy, in charge, in chief, in the ascendant,
   influential, key, key signature, keynote, leading, magisterial,
   main, major, major key, master, mediant, mighty, minim, minor,
   momentous, monocratic, musical note, natural, normal, note, number,
   official, on the throne, ordinary, outstanding, overbearing,
   overcoming, overriding, overruling, pandemic, paramount,
   patent note, pedal point, popular, potent, powerful, predominant,
   predominate, predominating, preeminent, premier, prepollent,
   preponderant, preponderate, prepotent, prestigious, prevailing,
   prevalent, primal, primary, prime, principal, prominent, puissant,
   quarter note, quaver, rampant, ranking, regnant, regulating,
   regulative, regulatory, reigning, report, responding note, rife,
   routine, ruling, running, semibreve, semiquaver, senior,
   shaped note, sharp, sixteenth note, sixty-fourth note, sovereign,
   spiccato, staccato, standard, star, stellar, stereotyped,
   subdominant, submediant, substantial, subtonic, successful,
   supereminent, superior, supertonic, supreme, surpassing,
   sustained note, swaying, tercet, thirty-second note, tonality,
   tone, tonic, tonic key, topflight, topmost, totalitarian,
   transcendent, triplet, triumphal, triumphant, uppermost, usual,
   vanquishing, victorious, weighty, whole note, winning



Bouvier's Law Dictionary, Revised 6th Ed (1856):

DOMINANT. estates. In the civil law, this term is used to signify the estate
to which a servitude or easement is due from another estate; for example,
where the owners of the estate, Blackacre, have a right of way or passage
over the estate Whiteacre, the former is called the dominant, and the latter
the servient estate. Bouv. Inst. n. 1600.