[18C+] the mouth.
[2000s] a chatterer.
[late 18C–early 19C] a bridle.
see blow one’s gob off under gob n.1
[mid-18C–1910s] to inform, to betray.
[early 19C] to talk, esp. to brag, to boast.
[early 19C] to show off, to act ostentatiously.
[late 18C–early 19C] to betray a secret, to inform against.
[late 19C_1930s] to talk excitedly.
see shut (up) one’s gob under gob n.1
[1910s–20s] to talk a language.
[late 18C-late 19C] be quiet!