of the third order, rank, stage, formation, etc.; third.
Chemistry. A. noting or containing a carbon atom united to three other carbon atoms. B. formed by replacement of three atoms or groups.
(initial capital letter) Geology. 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.
Ecclesiastical. 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).
(initial capital letter) Geology. the Tertiary Period or System.
Ornithology. a tertial feather.
(often initial capital letter) Ecclesiastical. a member of a tertiary branch of a religious order.
For it was impossible not to be sensible, that, while these three characters figured so largely on my private theatre, I — though probably reckoned as a friend by all — was at best but a secondary or tertiary personage with either of them.
-- Nathaniel Hawthorne, The Blithedale Romance, 1852
She'd explained all of this the last couple of days to various out-of-town cops who'd volunteered to take over the secondary and tertiary policing duties of the city.
-- Jay McInerney, The Good Life, 2007
He might dissect, anatomize, and give names; but, not to speak of a final cause, causes in their secondary and tertiary grades were utterly unknown to him.
-- Mary Shelley, Frankenstein, 1818
Since entering English in the mid 1500s, tertiary, which comes from the Latin tertius meaning "third," has been applied as a technical term for many different subject matters.