A person who talks too much and often too loudly, especially someone who boasts or expresses opinions aggressively.
Compound word from 'loud' (high volume) and 'mouth' (the organ of speech), combined as a descriptor for someone with a loud, noisy mouth. Entered English slang in the 1800s.
Compound insults like 'loudmouth,' 'bigmouth,' and 'motormouth' are all describing the same annoying person but emphasizing different aspects—noise level, arrogance, or non-stop talking.
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