Green’s Dictionary of Slang

1. to reduce verbal or psychological pressure.

1936		D. Burley in Chicago Defender 20 June 10: We’ll lighten up a bit and be kind to the folks.
1967		M. Braly On the Yard (2002) 158: If it were a gambling debt, some bet you lost, I might lighten up. I write off a lot of bad paper.
1971		E.E. Landy Underground Dict. (1972).
1981		H. Gould Fort Apache, The Bronx 98: Lighten up on the dude.
1987		(con. 1967) Bunch & Cole Reckoning for Kings (1989) 132: Hey. Lighten up. I got a blister is all.
2000		P. Beatty Tuff 251: Lighten up on them, Ms. Nomura, dag.

2. (orig. US black) to calm down.

1946		A. Rivkin Till End of Time [film script] When she lightens up she can write me a long letter [HDAS].
1970		C. Major Dict. Afro-Amer. Sl.
1977		N.C. Heard When Shadows Fall 52: ‘[L]ighten up, baby. Remember where you were just a few short years ago.’.
1980		E. Folb Runnin’ Down Some Lines 53: I [...] tol’ ’em to lighten up ’cause I know ’im.
1997		C. Hiaasen Lucky You 93: JoLayne told him to lighten up.
2004		Mad mag. Oct. 45: Lighten up, Giuseppe.

3. to act more cheerfully, to cheer up.

1967		W. Manus Mott the Hoople 18: I laughed and rumpled her hair. ‘Come on, baby. Let’s lighten up.’.
1972		O. Hawkins Ghetto Sketches 15: Rudy! Rudy baby! Lighten up!
1986		W.D. Ehrhart Passing Time (1988) 69: Geez, how come I always have to make you have fun? Lighten up, will you?
1997		(con. 1970s) G. Pelecanos King Suckerman (1998) 73: Lighten up with that shit, okay?
2004		P. Howard PS, I Scored the Bridesmaids 37: Hey, lighten up, dude.
2018		G. Disher Kill Shot [ebook] Once or twice in his past a woman had slipped under his guard long enough to tell him he ought to lighten up.
2020		D. Winslow ‘The Last Ride’ in Broken 300: ‘You need to lighten up a bit there, Cal. It’s grim enough around here already’.

4. to cease from an action.

1973

D. Goines Street Players 186: Whenever the preacher lightened up to catch his wind.

5. to act more enthusiastically.

1998

I. Welsh Filth 38: I warned Carole she’d go the same wey if she didnae lighten up a bit on the shaggin front.

6. to diminish one’s input of a given substance or activity.

2001

J. Stahl Plainclothes Naked (2002) 2: Maybe you should lighten up on the rock, Cuz. You’re getting cranky.