(tûr′shē·er′ē, -shə·rē) adjective
1. Third in point of time, number, degree, or standing.
2. Tertial.
3. Eccl. Pertaining to the third order of a religious body.
4. Chem. a Having three substituted atoms or radicals: a tertiary amine, b Denoting a radical in which three bonds of the combining carbon atoms are directly connected with three other carbon atoms: tertiary butyl.
—noun plural ·ar·ies
1. Ornithol. One of the feathers attached to the humerus joint of the wing of a bird.
2. Any member of the third order of a monastic body. [<L tertiarius <tertius third]

(tur′shē·er′ē, -shə-rē) Geol. adjective
Of or pertaining to the earlier of the two geological periods or systems comprising the Cenozoic era, following the Cretaceous and succeeded by the Quaternary.
—noun The Tertiary period or system, characterized by the rise of mammals.