tertiary

adjective

• 1third in order or level:most of the enterprises were of tertiary importance the tertiary stage of the disease
• chiefly British relating to or denoting education at a level beyond that provided by schools, especially that provided by a college or university.
• relating to or denoting the medical treatment provided at a specialist institution.

• 2 (Tertiary) Geology of, relating to, or denoting the first period of the Cenozoic era, between the Cretaceous and Quaternary periods, and comprising the Paleogene and Neogene subperiods.

• 3 Chemistry (of an organic compound) having its functional group located on a carbon atom that is itself bonded to three other carbon atoms.
• Chemistry (chiefly of amines) derived from ammonia by replacement of three hydrogen atoms by organic groups.

noun

• 1 (the Tertiary) Geology the Tertiary period or the system of rocks deposited during it.

  The Tertiary lasted from about 65 million to 1.6 million years ago. The mammals diversified following the demise of the dinosaurs and became dominant, as did the flowering plants

• 2a lay associate of certain Christian monastic organizations:a Franciscan tertiary