- tertiary
- 1656, "of the third order, rank, degree, etc.," from L. tertiarius "of or pertaining to a third," from tertius "third." The geological sense (with capital T-) of "era after the Mesozoic" (which formerly was called the Secondary) is attested from 1794, after It. terziari, used in this sense 1760 by It. geologist Giovanni Arduino (1714-1795).