(n.) An accessory plume arising from the posterior side of the stem of the contour feathers of many birds; -- called also aftershaft. See Illust. of Feather.
Webster's Revised Unabridged Dictionary
| APA | Webster's. (2011). hypoptilum. Retrieved September 21, 2026, from http://smartdefine.org/hypoptilum/definitions/2018465 |
| Chicago | Webster's. 2011. "hypoptilum" http://smartdefine.org/hypoptilum/definitions/2018465 (accessed September 21, 2026). |
| Harvard | Webster's 2011, hypoptilum, Smart Define, viewed 21 September, 2026, <http://smartdefine.org/hypoptilum/definitions/2018465>. |
| MLA | Webster's. "hypoptilum" 27 May 2011. Web. 21 September 2026. <http://smartdefine.org/hypoptilum/definitions/2018465> |