Green’s Dictionary of Slang

1. (also loosen it up) to relax, esp. as an imper.

1896		Ade Artie (1963) 9: I went in, thinkin’ I might get ’em loosened up and pull out the price of a Christmas present for the girl.
1917		Boy’s Own Paper XL:2 59: Jes’ loosen up an’ tell me how you an’ Waseche ain’t up on Ten Bow workin’ yer claim?
1933		W.R. Burnett Dark Hazard (1934) 64: After the fourth stein, Jim began to loosen up.
1942		R. Chandler High Window 138: At first he laughed in my face, but when I told him [...] that she would certainly set the police on him when I told her where the coin was, then he loosened up.
1950		‘Hal Ellson’ Tomboy (1952) 116: Loosen up [...] you’re dreaming, baby.
1966		R. Stone Hall of Mirrors (1987) 50: Whaddya say sport, loose it up one time — Mother need never know, sport—.
1979		E. Torres After Hours 149: I was [...] beginnin’ to loosen up.
1989		C. Hiaasen Skin Tight 62: The black kids loosened up a little.
1993		I. Welsh Trainspotting 41: Loosen up fir fuck sakes! It’s New fuckin Year!
2000		Observer 5 Mar. 🌐 When I met Herzog in Cologne last week, the city was preparing to put on its party clothes for Carnival, a five-day, drink-driven revel that loosens up even the stuffiest of Rhinelanders.

2. as loosen up on, to relax one’s restraints on another .

1915

Van Loan ‘Sporting Doctor’ in Taking the Count 35: If he doesn’t loosen up on me a little bit, I’m going to beat it.

3. to start speaking, esp. as an imper.

1908		B. Fisher A. Mutt in Blackbeard Compilation (1977) 34: I can give you the low down on A. Mutt as I think I can induce the spirits to loosen.
1917		Boy’s Own Paper XL:4 214: Come on, now – loosen up!
1959		E. De Roo Go, Man, Go! 124: Pa was absolutely not speaking to him for the first few miles. Then he loosened up.

4. to spend or hand over money [to loosen one’s purse-strings].

1896		H. Blossom Checkers 231: I ‘loosened.’ Well, perhaps he’ll do me a good turn some time.
1908		B. Fisher A. Mutt in Blackbeard Compilation (1977) 57: Dame Rumor has it that Atty. Beany is going to loosen on some of Pickels’ dough and buy himself a home.
1908		K. McGaffey Sorrows of a Show Girl Ch. i: ‘For Heaven’s sake, order wine,’ ‘Please loosen up and order wine.’.
1917		Van Loan ‘The Redemption Handicap’ in Old Man Curry 184: Do you know what that piker wanted to bet? Six dollars [...] I made him loosen up for fifteen.
1928		M.C. Sharpe Chicago May (1929) 69: He got twenty-five dollars a week, with odd amounts thrown in when he could cajole the family into loosening up.
1938		D. Runyon ‘Pick the Winner’ in Runyon on Broadway (1954) 318: The professor is a nice guy, but [...] he does not loosen so easy.