adj. & n.
adj. 1 third in order or rank etc. 2 (Tertiary) Geol. of or relating to the first period in the Cenozoic era with evidence of the development of mammals and flowering plants (cf. PALAEOCENE, EOCENE, OLIGOCENE, MIOCENE, PLIOCENE). °Cf. Appendix II.
n. 1 Geol. this period or system. 2 a member of the third order of a monastic body. tertiary education education, esp. in a college or university, that follows secondary education.
[ L tertiarius f. tertius third ]