The Collaborative International Dictionary
Tertiary \Ter"ti*a*ry\, a. [L. tertiarius containing a third part, fr. tertius third: cf. F. tertiaire. See Tierce.]
Being of the third formation, order, or rank; third; as, a tertiary use of a word.
--Trench.(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.
(Geol.) Later than, or subsequent to, the Secondary.
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(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.)
The first period of the age of mammals, or of the Cenozoic era.
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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.
Usage examples of "tertiary age".
The fishes of the Palaeozoic age are in no respect the ancestors of the reptiles of the Secondary age, nor does Man descend from the mammals which preceded him in the Tertiary age.
But at its feet the great beasts of the Tertiary Age still haunted its lower regions.