/terr"shee er'ee, terr"sheuh ree/ , adj., n., pl. tertiaries .
adj.
1. of the third order, rank, stage, formation, etc.; third.
2. Chem.
a. noting or containing a carbon atom united to three other carbon atoms.
b. formed by replacement of three atoms or groups.
3. ( cap. ) Geol. noting or pertaining to the period forming the earlier part of the Cenozoic Era, occurring from 65 million to 2 million years ago, characterized by the development and proliferation of mammals. See table under geologic time .
4. Ornith. tertial.
5. Eccles. noting or pertaining to a branch, or third order, of certain religious orders that consists of lay members living in community (regular tertiaries) or living in the world (secular tertiaries) .
n.
6. ( cap. ) Geol. the Tertiary Period or System.
7. Ornith. a tertial feather.
8. ( often cap. ) Eccles. a member of a tertiary branch of a religious order.
9. See tertiary color .
[ 1540-50; tertiarius of third part or rank, equiv. to terti ( us ) THIRD + -arius -ARY ]