1. Being of the third formation, order, or rank; third; as, a tertiary use of a word.
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. Zool. 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.
n : from 63 million to 2 million years ago [syn: Tertiary]