Green’s Dictionary of Slang

gasbag n.

also gasman
[gas n.1 (1)]

a talkative person.

[US]Ladies’ Repository (N.Y.) Oct. VIII:37 316/2: Gasman, a braggart.
[US]J.W. Haley Rebel Yell and The Yankee Hurrah (1985) 250: He was a cheap buffoon and the very prince of gasbags.
[US]Newton Kansan 2 Jan. 2/3: Gas bags were never known to do more than make a noise [DA].
W. Kansas World (Wakeeny, KS) 3 Oct. 1/4: ‘Capt.’ Glaspie is the worst old blister west of the Alleghanies. His talk is foul and indecent. He is commonly known as the Pawnee ‘gasbag’.
[UK]Referee 6 Jan. n.p.: That great gas-bag of modern days [F&H].
[Aus]Truth (Sydney) 17 Mar. 6/4: Had Patrick got John L. into the ring, the Maitlander would have been champion instead of the gas-bag that now poses as boss of the world.
[UK]Binstead & Wells Pink ’Un and Pelican 186: That vain old gasbag, Sir William Vernon Harcourt.
[US]‘O. Henry’ ‘The Clarion Call’ Voice of the City (1915) 195: Kind of rattles you, doesn’t it, to have the mysterious villain call up [...] and tell you what a helpless old gas-bag you are?
[US]J.C. Lincoln Shavings 16: I judge likely I’m the ‘this’ you and that gas bag have been talkin’ about.
[UK]E. Raymond Tell England (1965) 83: Kick that gas-bag Pennybet out.
[Aus]Townsville Daily Bull. (Qld) 10 Aug. 16/2: One old gasbag said there was no disease or trouble.
[UK]E. Raymond Child of Norman’s End (1967) 362: A trifler, and a gas-bag to boot.
[US]O. Strange Sudden Takes the Trail 62: You ain’t scared o’ that gas-bag, are you?
[US]S. Lewis World So Wide 163: I’m going to collect as many facts [...] as that old gas-bag, Belfont, has in maybe twenty years.
[UK]I. & P. Opie Lore and Lang. of Schoolchildren (1977) 68: One who talks too much (i.e. a chatter-box, gas-bag, [...] or wind-bag).
[US]K. Kolb Getting Straight 77: Poor old gasbag.
[UK]D. Nobbs Fall and Rise of Reginald Perrin (1976) 142: What have you two gas bags been talking about?
[US]H. Rawson Dict. of Invective (1991) 170: The person who talks too much is, naturally, a gasbag.
[Aus]G. Seal Lingo 2: Although mostly taken for granted, the importance of the vernacular in everyday life is apparent from the number of Lingoisms describing or referring to it. chinwag; gasbag; have a yarn; bend your ear.