motormouth means one who talks very quickly or incessantly; a chatty or loquacious person. Lexicurio rates it Sui generis — a strength score of 87 out of 100.
Etymology
From motor + mouth, from the figurative notion that the mouth moves so much that it seems motorized.
noun
- One who talks very quickly or incessantly; a chatty or loquacious person.“He's such a motormouth that I can never get a word in.”
verb
- To talk very quickly or incessantly.