of the third order, rank, stage, formation, etc.; third.
Chemistry. noting or containing a carbon atom united to three other carbon atoms. 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)