over-under

[ oh-ver-uhn-der ]
/ ˈoʊ vərˈʌn dər /

adjective

(of double-barreled firearms) with one barrel mounted over the other.

noun

such a firearm.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

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British Dictionary definitions for over-under

over-under

/ US /

adjective

(of a two-barrelled firearm) having one barrel on top of the other

noun

an over-under firearm
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012