Green’s Dictionary of Slang

(US) a synon. for god-damn adj./god-damned adj.

1884		Dly Bulletin (HI) 5 July 3/3: The rule o’ that wash house air ‘No checky. no washy,’ an’ I’m dad gummed if they don’t enforce it.
1894		Kansas Agitator (Garnett, KS) 31 May 5/1: ‘Well, I’ll be dad-gummed!’ exclaimed the old gent.
1904		N.Y. Tribune 6 Nov. 18 /3: You may take that dad-gummed fire escape and chop it up.
1913		Bryan Dly Eagle (TX) 20 Nov. 2/2: We are comforted by the fact that other places are in a dad gummed sight worse fix.
1921		Concordia Sentinel (Vidalia, LA) 12 Feb. 4/1: Mr Editor, it is a ‘dad gummed’ fact!
1932		J.C. Rogers ‘Where the Heart Lies’ in Botkin Folk-Say 155: I think it’s a dad-gummed good place to be.
c.1935		‘She Will Be Coming Around the Mountain’ [comic strip] in B. Adelman Tijuana Bibles (1997) 51: So I caught you dad’gum shif’less skonk a friggin my gal.
1943		W. Guthrie Bound for Glory (1969) 19: I’m th’ best dadgum blacksmith in Logan County!
1944		T.D. Clark Pills, Petticoats and Plows 156: There was a sentiment that ‘a dad-blamed hog and a dad-gummed cow were the most aggravating things that ever made tracks on a piece of cotton land’ [DA].
1946		(con. 1910s) J. Thompson Heed the Thunder (1994) 243: Take your dadgummed trade somewheres else, and see if I care.
1954		(con. 1920s–30s) J.O. Killens Youngblood (1956) 247: Put a crease in them scounds so keen cut your dadgum fingers off.
1966		‘Tom Pendleton’ Iron Orchard (1967) 321: Leave off that dad-gum diaphragm do-majig, or whatever it is that keeps babies away.
1973		J. Yount Trapper’s Last Shot (1974) 203: ‘Stop it whoop dadgum you let me get off of it I get aholt whoop stop it!’ she yelled.
1994		Indep. Mag. 6 Aug. 36: We had three large groups come over last month, but it’s been pretty dadgum quiet since then.
2012		R.A. Dickey Wherever I Wind Up 170: [T]hat weirdo pitch we throw. [...] You just can’t trust it. Because it’s a dadgum knuckleball.