Green’s Dictionary of Slang

a fool, a simpleton; also as a term of address.

1796		T.G. Fessenden ‘Rustic Revel’ Poems (1804) 17: Pious deacon would, no doubt, / Beat it into many a thick-head / That our junketing is wicked.
1825		Pierce Egan’s Life in London 20 Feb. 28/2: A dandy, after paying a shilling for his letter, was laughed at by his friends in reading the direction, for Jonathan Thickhead, Esq.
[1837		Leeds Times 14 Oct. 4/1: He need not trouble his thickhead any more with mere paper spite].
1839		Northern Liberator (Tyne & Wear) 28 Sept. 4/4: My dear Squire Thickhead...
1840		T. Haliburton Clockmaker III 218: Now do you onderstand, says she, you thick head, you?
1853		Leeds Times 29 Oct. 8/1: ‘You great thick-head, if you don’t get to bed, I’ll pause your — ’.
1862		Bury Times 12 July3/3: A young man [...] complained that Mr Barker had spoken of one of his opponents as [...] a thickhead.
1871		Manchester Eve. News 27 Nov. 2/1: Mr Gladstone replied [...] that he was an inconceivable thickhead.
1881		Portsmouth Eve. News 19 Apr. 2/4: The two little girls belonging to the complainant wrote ‘Thick-head’ on defendant’s wall.
1889		Dundee Courier 25 Jan. 6/5: Cleary’s father said his boy was a ‘thick-head,’ and could not take up his education.
1894		G. du Maurier Trilby 65: What for a thick head! what for a pigdog!
1905		Marvel III:62 24: What the blazes are you doin’, thickhead?
1911		G. Bronson-Howard Enemy to Society 288: You, you chumps, you thick heads, you snivelling, drivelling fools, you’ll wear striped suits and wield pickaxes and answer to a number.
1920		Barrier Miner (Broken Hill, NSW) 6 Feb. 2/7: A few learned shrewd nuts have accused us numbskulls and thick-heads of being misled by the officials of that big ‘red-ragger’ association.
1929		R.H.H. Nichols ‘Sinbad the Sailor’ Fight Stories Jan. 🌐 Don’t you see what it is, you thick-head?
1936		J.T. Farrell World I Never Made 179: He’d just like to tell that thickhead a thing or two.
1942		G. Casey It’s Harder for Girls 25: You’re a bit of a thickhead, Jack.
1952		(con. 1948) G. Mandel Flee the Angry Strangers 186: You swine of a thickhead!
1959		I. & P. Opie Lore and Lang. of Schoolchildren (1977) 201: A ‘thick-head’, with a ‘head full of lead.’.
1970		G.F. Newman Sir, You Bastard 203: He was just a thickhead incapable of comprehending.
1981		P. Reading ‘The Euphemisms’ Tom O’Bedlam’s Beauties 42: Addle/Silly/Chuckle/Dunder/Sap/Bone/Block/Thick/Muddle/Crack- / Heads.
1998		P. Bailey Kitty and Virgil (1999) 127: I must tell you how the thickhead hunted a bear.
2009		P. Temple Truth 78: Could be family, the thickheads stick close to home.