Tertiary period Meaning, Definition & Usage

  1. noun from 63 million to 2 million years ago
    Tertiary.

WordNet

Definitions
  1. . (Geol.) (a) The first period of the age of mammals, or of the Cenozoic era. (b) The rock formation of that period; called also Tertiary formation. See the Chart of Geology.

Webster 1913