Source : Webster's Revised Unabridged Dictionary (1913)

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.

   2. (Geol.) The Tertiary era, period, or formation.

   3. (Zo["o]l.) One of the quill feathers which are borne upon
      the basal joint of the wing of a bird. See Illust. of
      {Bird}.

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.

   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}.

Source : WordNet®

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