What does "motormouth" mean?

One who talks very quickly or incessantly; a chatty or loquacious person.

Motormouth

Common synonyms include: blabbermouth, chatterbox, chatty, dominant talker, excessive talker, garrulous.

noun, verb, slang

noun, verb, slang ·Moderate ·College level

Noun

1
One who talks very quickly or incessantly; a chatty or loquacious person. informal
"He's such a motormouth that I can never get a word in."
2
someone who talks incessantly wordnet

Verb

"He's such a motormouth that I can never get a word in."

From motor + mouth, from the figurative notion that the mouth moves so much that it seems motorized.