Tertiary

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. [ 1913 Webster ]

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. [ 1913 Webster ]

3. (Geol.) Later than, or subsequent to, the Secondary. [ 1913 Webster ]

4. (Zool.) Growing on the innermost joint of a bird's wing; tertial; -- said of quills. [ 1913 Webster ]

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. [ 1913 Webster ]