Green’s Dictionary of Slang

(US) beyond measure, immeasurably, excessively.

1845		W.T. Thompson Chronicles of Pineville 108: Here’s a business! But that’s always the way with you – there’s everlastin’ly something happenin’ whenever —.
1855		J. Brougham Basket of Chips 374: It is so everlastingly a boastin’ of its refinement.
1883		Sweet & Knox On a Mexican Mustang, Through Texas 229: I’m everlastingly sorry.
1887		H. Frederic Seth’s Brother’s Wife 107: You just everlastingly gave it to that snide show to-night.
1889		Century Mag. (N.Y.) 2040/3: He is everlastingly stingy [DA].
1902		Laurens Advertiser (SC) 15 Jan. 4/4: You help us everlastingly lick them [...] and you can say [etc.].