[ter.tia.ry] n, pl -ries (ca. 1550) 1 [ML tertiarius, fr. L, of a third]: a member of a monastic third order esp. of lay people
2. cap: the Tertiary period or system of rocks
[2]tertiary adj [L tertiarius of or containing a third, fr. tertius third] (ca. 1656) 1 a: of third rank, importance, or value b chiefly Brit: of, relating to, or being higher education c: of, relating to, or constituting the third strongest of the three or four degrees of stress recognized by most linguists (as the stress of the third syllable of basketball team)
2. cap: of, relating to, or being the first period of the Cenozoic era or the corresponding system of rocks marked by the formation of high mountains (as the Alps, Caucasus, and Himalayas) and the dominance of mammals on land--see geologic time table 3 a: involving or resulting from the substitution of three atoms or groups "a ~ salt" "~ amine" b: being or containing a carbon atom having bonds to three other carbon atoms "an acid containing a ~ carbon" "~ alcohols"
4: occurring in or being a third stage: as a: being or relating to the recovery of oil and gas from old wells by means of the underground application of heat and chemicals b: being or relating to the purification of wastewater by removal of fine particles, nitrates, and phosphates