1. Third in place, order, degree, or rank.
2. Of, relating to, or designating the short flight feathers nearest the body on the rear edge of a bird's wing.
a. Of, relating to, or having a carbon atom that is attached to three other carbon atoms in a molecule.
b. Of or relating to the replacement of three of several atoms or groups in a compound, such as an amine in which three valences of the functional group are taken by carbon atoms.
c. Of or relating to salts of acids containing three replaceable hydrogen atoms.
4. Tertiary Of, relating to, or being the period of geologic time from about 66 to about 2.6 million years ago, the older of the two periods of the Cenozoic Era. The Tertiary Period is characterized by the appearance of modern flora, insects, fish, amphibians, and reptiles, and by the dominance of mammals as vertebrate life forms on land. See Table at geologic time.
n. pl. ter·ti·ar·ies
1. A tertiary feather.
2. Tertiary The Tertiary Period.
3. Roman Catholic Church A member of a religious Third Order.
[Latin tertiārius, from tertius, third; see trei- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.