Of third rank or order; subsequent. / (chemistry) Possessing some quality in the third degree; especially having been subjected to the substitution of three atoms or radicals.

Any item considered to be of third order. / A tertiary colour. / (geology) Something from the Tertiary Period (the former term for the geologic period from 65 million to 2.58 million years ago).

(geology) Of or pertaining to the first part of the Cenozoic era when modern flora and mammals appeared.

(geology) The first part of the Cenozoic era when modern flora and mammals appeared.

plural of tertiary

(organic chemistry) An amine, containing three radicals, of general formula R₁R₂R₃-N; the radicals may be the same, different, or part of a ring.

(organic chemistry) The univalent organic radical (CH₃)₃C-

(chemistry) any compound of general formula PR₃ (where R is not H)

(chemistry) Any alcohol of general formula R₃C-OH

plural of tertiary amine