\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}.
3. (Geol.) Later than, or subsequent to, the Secondary.
4. (Zo["o]l.) Growing on the innermost joint of a bird's
   wing; tertial; -- said of quills.
{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.

\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}.