Meaning

noun from 63 million to 2 million years ago

adjective coming next after the second and just before the fourth in position

originPIE word *tréyes Borrowed from the Latin tertiārius (“of the third part or rank”), from tertius (“third”) (from Proto-Indo-European *tr̥tyós, whence English third) + -ārius (whence the English suffix -ary); compare the French tertiaire. By surface analysis, terti- + -ary.

Etymology from Wiktionary, CC BY-SA 3.0