Green’s Dictionary of Slang

(US black) covert, secret.

1997–2000		College Sl. Research Project (Cal. State Poly. Uni., Pomona) 🌐 DL (down low) (d/o) (adj.) Down low; secret.
2000		Ebonics Primer at www.dolemite.com 🌐 down low (also D-L) Definition: subversive, so know one will know. Example: The cops is after me, so’s i got to keep my shit on the down low.
2002		Teen Lingo: The Source for Youth Ministry 🌐 down low or D.L Secret, keep it a secret, not public information. ‘Jesse just broke up with Stacey . . . keep it down low.’.
2010		A. Steinberg Running the Books 307: A real pimp always keeps it low down and down low.
2011		G. Hayward Corruption Officer [ebk] cap. 11: There are so many offices and down low spots in here, you can get a quickie in broad day light.