Green’s Dictionary of Slang

gab n.1

[Scot. gab, the mouth]

[18C+] the mouth.

In compounds

gab-box (n.)

[2000s] a chatterer.

gab string (n.) (also gob string) [gob n.1 (1)]

[late 18C–early 19C] a bridle.

In phrases

blow the gab (v.)

[mid-18C–1910s] to inform, to betray.

flash one’s gab (v.)

[early 19C] to talk, esp. to brag, to boast.

flash the gab (v.)

[early 19C] to show off, to act ostentatiously.

give the gab (v.)

[late 18C–early 19C] to betray a secret, to inform against.

shoot one’s gab off (v.) (also shoot off one’s gab)

[late 19C_1930s] to talk excitedly.

sling a gab (v.)

[1910s–20s] to talk a language.

In exclamations

stop your gab! (also hold your gab!)

[late 18C-late 19C] be quiet!