Green’s Dictionary of Slang

blether n.

[ME blather, nonsense; thus synon. Scot. blether; Irish bladar, flattery]

1. (also bletherhead, blethers) one who talks nonsense.

[UK]W.H. Smyth Sailor’s Word-Bk (1991) 107: Blether-Head. A blockhead. Blethering. Talking idle nonsense; insolent prate.
[UK] ‘Under the Harrow’ in ‘F. Anstey’ Mr Punch’s Model Music Hall 139: Characters. Sir Poshbury Puddock (a haughty and high-minded Baronet) [...] Blethers (an ancient and attached Domestic).
Lichfield Mercury 6 June 3/3 What made you follow me, you bletherhead?:
[Ire]L. Mackay Mourne Folk 19: Och, Dandy, ye’re a blether; but I forgive ye, for ye’re too ould to take any notice of.

2. a chat.

[Scot]I. Welsh Glue 46: A wee beer n a blether.
[Scot](con. 1980s) I. Welsh Skagboys 160: Wir gaun doon thaire tae huv a wee fuckin blether wi this Hong Kong Fuey cunt.
[Scot]I. Welsh Decent Ride 283: Thanks for the blether. It’s helped.

In derivatives

bletherheaded (adj.)

absurd, nonsensical.

[UK]Leeds Times 26 Jan. 8/3: The Bletherheaded Band — Perhaps never before had any band so singular a title, but in itself it is the greatest wonder of all.
[UK]Leeds Times 1 Jan. 2/5: Troupes of revellers were abroad in motley dresses, who marched about with bletherheaded bands.
[UK]Notts. Guardian 30 Mar. 12/3: You will understand what a time this bletherheaded Scot has led me. He was always a saucy upstart.