D defs.my
Entry 1 sense Webster, 1913

Oligocene

/äl'-əg-ōs-ēnˌ/ · Ol·i·go·cene · IPA /ˈɑləɡoʊsˌiːn/
01 a. Of, pertaining to, or designating, certain strata which occupy an intermediate position between the Eocene and Miocene periods.
  1. 1.
    Of, pertaining to, or designating, certain strata which occupy an intermediate position between the Eocene and Miocene periods.(Geol.)