motor-mouth

[ moh-ter-mouth ]
/ ˈmoʊ tərˌmaʊθ /

noun, plural mo·tor-mouths [moh-ter-mouths, mouth z] /ˈmoʊ tərˌmaʊθs, ˌmaʊðz/. Slang.

a person who is a constant or irrepressible talker.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for motormouth

motormouth

/ (ˈməʊtəˌmaʊθ) /

noun

slang a garrulous person
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