The Collaborative International Dictionary of English v.0.48:

Tertiary \Ter"ti*a*ry\, a. [L. tertiarius containing a third
   part, fr. tertius third: cf. F. tertiaire. See Tierce.]
   1. Being of the third formation, order, or rank; third; as, a
      tertiary use of a word. --Trench.
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   2. (Chem.) Possessing some quality in the third degree;
      having been subjected to the substitution of three atoms
      or radicals; as, a tertiary alcohol, amine, or salt. Cf.
      Primary, and Secondary.
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   3. (Geol.) Later than, or subsequent to, the Secondary.
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   4. (Zool.) Growing on the innermost joint of a bird's wing;
      tertial; -- said of quills.
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   Tertiary age. (Geol.) See under Age, 8.

   Tertiary color, a color produced by the mixture of two
      secondaries. "The so-called tertiary colors are citrine,
      russet, and olive." --Fairholt.

   Tertiary period. (Geol.)
      (a) The first period of the age of mammals, or of the
          Cenozoic era.
      (b) The rock formation of that period; -- called also
          Tertiary formation. See the Chart of Geology.

   Tertiary syphilis (Med.), the third and last stage of
      syphilis, in which it invades the bones and internal
      organs.
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The Collaborative International Dictionary of English v.0.48:

Tertiary \Ter"ti*a*ry\, n.; pl. Tertiaries.
   1. (R. C. Ch.) A member of the Third Order in any monastic
      system; as, the Franciscan tertiaries; the Dominican
      tertiaries; the Carmelite tertiaries. See Third Order,
      under Third. --Addis & Arnold.
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   2. (Geol.) The Tertiary era, period, or formation.
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   3. (Zool.) One of the quill feathers which are borne upon the
      basal joint of the wing of a bird. See Illust. of Bird.
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WordNet (r) 3.0 (2006):

tertiary
    adj 1: coming next after the second and just before the fourth
           in position [syn: third, 3rd, tertiary]
    n 1: from 63 million to 2 million years ago [syn: Tertiary,
         Tertiary period]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "tertiary":
   Maxwell triangle, Munsell scale, chromatic circle,
   chromatic spectrum, chromaticity diagram, color circle,
   color cycle, color index, color mixture curve, color solid,
   color spectrum, color system, color triangle, complementary color,
   covert, demitint, feather, feathers, full color,
   fundamental colors, hackle, half tint, halftone, hue cycle, mail,
   metamer, monochrome, plumage, primary, primary color, pure color,
   secondary, secondary color, solar spectrum, spectral color,
   spectrum, spectrum color, speculum, tertiary color, third