adjective

1. of the third rank, order, formation, stage, etc.; third
2. Chem.
   1. third in order or type; involving the substitution of three atoms or radicals
   2. characterized by or designating a carbon atom or group attached to three other carbon atoms or groups in a chain or ring
3. Geol. designating or of the first geologic period of the Cenozoic Era, usually subdivided into the Paleogene and the Neogene and characterized by the formation of major mountain ranges, the first grasses and grasslands, and the development of mammals as the dominant animal
4. Linguis.
   1. designating, of, or being the third strongest of the four phonemic degrees of stress
   2. a mark used to indicate this
5. R.C.Ch. of a Third Order
6. Zool. tertial

Etymology: L tertiarius < tertius, third

noun pl. tertiaries -·ar′·ies

1. R.C.Ch. a member of a Third Order
2. Zool. tertial