- (a.) Of, pertaining to or designating, certain strata which occupy an intermediate position between the Eocene and Miocene periods.
- (n.) The Oligocene period. See the Chart of Geology.
Webster's Revised Unabridged Dictionary
| APA | Webster's. (2011). oligocene. Retrieved September 23, 2026, from http://smartdefine.org/oligocene/definitions/2038656 |
| Chicago | Webster's. 2011. "oligocene" http://smartdefine.org/oligocene/definitions/2038656 (accessed September 23, 2026). |
| Harvard | Webster's 2011, oligocene, Smart Define, viewed 23 September, 2026, <http://smartdefine.org/oligocene/definitions/2038656>. |
| MLA | Webster's. "oligocene" 27 May 2011. Web. 23 September 2026. <http://smartdefine.org/oligocene/definitions/2038656> |