Green’s Dictionary of Slang

extremely, excessively, e.g. mortal cold, mortal drunk.

c.1407		Lydgate Reson and Sensuallyte (1965) 3665: The pereyl ys so mortal strong .
1625		Bacon Essays ‘Of Envy’ n.p.: Adrian the Emperour mortally envied poets and painters [F&H].
1668		Dryden An Evening’s Love Act III: I am mortally offended with you.
1712		J. Arbuthnot Hist. of John Bull 46: There was an old grudge between her and Sir Roger, whom she mortally hated.
a.1735		Granville quoted in Jonson n.p.: I mortally dislike a damning face [F&H].
1761		G. Colman Jealous Wife III i: I hate her mortally.
1771		Smollett Humphrey Clinker (1925) I 37: His pupil, who seemed to be about the age of threescore, stooped mortally.
1772		Bridges Burlesque Homer (3rd edn) 181: If he’s mortal rogue, let’s beat him.
1795		Sporting Mag. Nov. VII 81/1: Your ale was moretal good.
1804		Sporting Mag. Jan. XXIII 228/1: I’m mortal glad you’ve come.
1825		T.C. Croker Fairy Legends and Traditions of the South of Ireland (1862) 287: The night was mortal cold.
1827		J.J. Stafford Love’s Frailties II i: I be mortal weak and faint – eh!
1827		T. Morton A School For Grown Children III i: Ice! – aye that’s what makes this place so mortal slippery.
1838		D. Jerrold Men of Character I 48: I was mortal certain I should find him here.
1843		T. Haliburton Sam Slick in England II 89: One mortal brilin’ hot day, as I was a pokin’ along the road.
c.1850		F.M. Whitcher Widow Bedott Papers (1883) 34: I never could bear Tim Crane – he’s so mortal mean.
1850		W.K. Northall Life and Recollections of Yankee Hill 22: Wal, this is a plaguey nice place; and what a mortal lot of purty picters you’ve got hanging round.
1855		Bell’s Life in Sydney 17 Mar. 3/1: It’s mortial hard I’ve worked at his gardin, the ommaghaun!
1876		Besant & Rice Golden Butterfly III 13: You get mortal tired of settin’ on end.
1886		R.L. Stevenson Kidnapped 40: I’m mortal hungry.
1887		H. Caine Deemster I 142: It’s morthal strange the way a man of your common sense can’t see that you’d wallop that squeaking ould Jemmy Quirk in a jiffy.
1889		C. Deveureux Venus in India I 31: Don’t offer her any rupees or you will offend her mortally.
1890		Kipling ‘The God from the Machine’ in Soldiers Three (1907) 7: Wan day, bein’ mortial idle [...] the rig’mint gave amsure theatricals.
1898		E. Pugh Tony Drum 88: It’s mortal dark, Michael. When’ll the moon be up?
1908		Denton (MD) Journal 7 Mar. 3/8: They’d ha’ been mortal like him if they’d been shaved.
1908		L. Doyle Ballygullion 129: He gives [...] a ‘hear, hear,’ wi’ a mortial bad hiccup between the ‘hears’.
1911		G. Stratton-Porter Harvester 378: You do look mortal tired.
1911		Truth (Sydney) 5 Mar. 11/3: Them there female’s mortal bad, sir, / For young girls to get among.
1914		G.A. England ‘Rural Locutions of Maine and Northern New Hampshire’ in DN IV:ii 76: mortal, mortial, adv. Very. ‘She was mortal hum’ly.’.
1925		L. Mackay Mourne Folk 106: I cud see nothin’; it was a mortial dark night; but just then at Glenoughlan school schoolhouse the moon came out of the clouds.
1925		L. Doyle Dear Ducks 19: A mortal fine girl she was, too.
1936		(con. 1830s–60s) ‘Miles Franklin’ All That Swagger 147: You are mortal uneasy about her accusations.
1940		O. Strange Sudden Takes the Trail 248: He was hurt mortal.
1943		G.A. Little Malachi Horan Remembers 11: Like his master, he had been mortal old and mortal wise. Now he was dead.
1943		W. Guthrie Bound for Glory (1969) 360: California’s mortally loaded down with stuff to ride along an’ look at, ain’t it?
1948		Z.N. Hurston Seraph on the Suwanee (1995) 865: I come here to get satisfaction for being mortal hurt on your rotten property.
1963		M. Braly Shake Him Till He Rattles (1964) 50: I figure I owe myself a little taste just to see what the shouting’s all about. I’d mortally hate to overlook something.
1967		M. Braly On the Yard (2002) 5: She was so mortally homely Red figured she’d come near scaring a dog off a gut wagon.
1978		S. King Stand (1990) 808: They hurt her gums mortal bad, but my! weren’t they tasty.
1998		A. Warner Sopranos 86: Chell gets home, pissed mortal, two or three in the morning.