Green’s Dictionary of Slang

(US black) ordinary, customary; also adv.

1931		Skip James ‘Hardtime killing Floor Blues’ 🎵 Let me tell you people just before I go, / These hard times will kill you just dry long so.
1934		Shamokin News-Dispatch (PA) 21 Mar. 4/4: Harlem isn’t much like that. Outwardly its existence is ‘dry long so’ — a peculiar xpression which means ordinary or uneventful .
1942		Morn. Herald (Uniontown, PA) 8 June 4/5: ‘Dry long so’ means fate, or that’s life for you.
1942		D. Burley N.Y. Amsterdam Star-News 25 July 14: I’m not so naive as to condemn all chicks ‘dry long so’.
1954		(con. 1920s–30s) J.O. Killens Youngblood (1956) 519: A negro is tough. Can’t kill him just dry along so. Especially your Daddy.
1980		J.L. Gwaltney Drylongso xxiii: Most black people are well within the ordinary, acceptable, drylongso standards of core black culture. [Ibid.] 33: Neither ugly nor pretty, just drylongso.
1987		Arizona Republican 7 Feb. 50/2: Gullah [...] used picturesque phrases, such as ‘day clean’ for morning and ‘dry long so’ for simple and direct.
2003		R. Guthrie Jr Race Music 222: I wish you could read something or see a movie that would show the people just, well, as my grandmother would say, drylongso.