blabbermouth

The word is a vivid Modern English compound, formed by combining two elements with clear semantic roles. The first element, 'blabber', is onomatopoeic, originating in Middle English to imitate the sound of rapid, nonsensical, or indiscreet chatter. The second element, 'mouth', is a native English word from Old English, referring literally to the physical organ. The compound's logic is transparently metaphorical: it characterizes a person not just by their action (blabbering) but by defining them as the source of that action—a mouth that blabs. This construction follows a classic Germanic pattern for creating expressive, often humorous or critical, agent nouns, painting a picture of someone whose primary defining feature is their indiscreet talkativeness.

Structure: blabber (to talk foolishly or excessively) + mouth (the bodily organ of speech) - blabber: Of imitative origin (Middle English blaberen), mimicking the sound of idle talk. Its functional role is the core action or behavior. - mouth: From Old English mūþ, meaning the opening in the face used for speaking and eating. Its functional role is the instrument or source of the action.