Green’s Dictionary of Slang

1. a small room, usu. occupied by a single man [SE f. 1900].

1771		Smollett Humphrey Clinker 5 June 3: So saying, he retreated into his den.
1816		W.T. Moncrieff All at Coventry I i: Oh, the luxury of scribbling twelve hours a day in the infernal den he called his office!
1845		Nat. Police Gaz. (NY) 6 Dec. 126/3: Cornelius Strain, the keeper of one of those ‘dens’ called junk shops.
1857		C. Kingsley Two Years Ago III 201: Mary lived in her own room, her father in his counting-house, or his ‘den’.
1868		L.M. Alcott Little Women II 149: I passed Mr. Bhaer’s room, where she was rummaging. ‘Did you ever see such a den, my dear?’.
1881		Newcastle Courant 16 Sept. 6/5: The police [...] knew that Nat and Sam had [...] been pal-ing and also that both were at the time staying at the den.
1882		Blackwood’s Mag. Dec. 709: [He] went off in the direction of his own den, a little room in which he smoked and kept his treasures .
1887		H. Frederic Seth’s Brother’s Wife 187: Nothing less like the bachelor’s den dear to tradition can be imagined.

2. (US Und.) one’s home, an establishment.

1781		R. King Modern London Spy 102: She was on her return [...] to her Den in Strutton’s Grounds.
1855		Yokel’s Preceptor 12: The outpourings of Mother Wood’s brothels; the two Jewesses; and the ‘young ladies’ of the infamous Mother Sparrow’s den.
1880		G.R. Sims Three Brass Balls 59: It is a strange house, this grimy den in Soho.
1890		Bulletin (Sydney) 5 July 5/4: [W]hen the police are proceeding against a man for having a lot of supposed-to-be stolen watches, etc., in his possession, the Herald breaks out into big print with ‘The Jewellery Haul,’ and goes on to speak of ‘the prisoner’s den,’ he being still legally innocent at the time. The word ‘haul’ in this connection means ‘catch,’ if it means anything at all, ‘den,’ as applied to a domicile, is undoubtedly understood to suggest its occupation by thieves.
1890		B.L. Farjeon Mystery of M. Felix I 154: He had lit the gas in his sitting-room [...] ‘This is my den, Sophy,’ he said.
1908		N.Z. Truth 22 Feb. 2/6: That dreadful drinking den, the Working Men’s Club.
1911		C.E. Mulford Bar-20 Days 147: I’d better tote a gun, goin’ down an’ beardin’ such a thief in his own den.
1924		P. Marks Plastic Age 172: It was Hugh’s first visit to a bootlegger’s den.
1937		Blind Boy Fuller ‘You Never Can Tell’ 🎵 Hey I met that woman’s second man / Right, right back in my den.
1944		‘Jiver’s Bible’ in D. Burley Orig. Hbk of Harlem Jive.
1958		Hughes & Bontemps Book of Negro Folklore 482: den: Apartment, room, house, home. All couples need their own den.
1962		B. Jackson Get Your Ass in the Water (1974) 174: The Baboon ran the joint, but it really Mr. Gorilla’s den.
1990		(con. early 1950s) J. Ellroy L.A. Confidential 378: One wall of his den was now a graph.

3. (US Und.) a prison (solitary confinement) cell.

c.1921		T. Norman Penny Showman 14: After about two hours in this den, the Black Maria arrived.
1950		Goldin et al. DAUL 57/2: Den. 1. (P) A cell.
1971		F. Hilaire Thanatos 147: Knock it off, Leslie. As a den mother, I don’t need you.
1999		D. Looser ‘Boob Jargon’ in NZEJ 13 29: den n.Cell.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 55/1: den n. 1 a cell 2 the solitary confinement punishment cell.