Green’s Dictionary of Slang

mortal adj.1

1. a general intensifier, e.g. all my mortal days.

[UK]Jonson Silent Woman IV v: cle.: Shall I goe fetch the Ladies to the Catastrophe? [...] daup.: By no mortall meanes.
[UK]Egan Finish to the Adventures of Tom and Jerry (1889) 85: The Squire is a mortal good man.
[US]C.A. Davis Letters of Major J. Downing (1835) 26: I don’t believe any one was drowned; but some did get a mortal ducking.
[UK]A. Mayhew Paved with Gold 123: Take me yourself to see her, and I’ll do any mortal thing you choose.
[US]G.W. Harris Sut Lovingood’s Yarns 299: When yu wake up, may yu fine hit tu be a mortal fac’.
[UK]J.K. Jerome Three Men in a Boat 57: Of course I had to turn every mortal thing out.
[US]P.L. Dunbar ‘The Rivals’ Lyrics of Lowly Life 63: An’ not a mortal word I knew / Of what the preacher preached er read.
[Aus]Sydney Sportsman (Surry Hills, NSW) 4 Sept. 3/3: There are a mortal lot of them, / Wot’s got no end of cheek.
[Ire]J.M. Synge Playboy of the Western World Act II: I can stay so, working at your side, and I not lonesome from this mortal day.

2. extreme, great.

[UK]R. L’Estrange Fables of Abstemius (1692) CCLXXXIX 260: The Birds were in a Mortal Apprehension of the Beetles.
Dryden Ovid I 733: The nymph grew pale, and in a mortal fright [F&H].
[UK]Vanbrugh & Cibber Provoked Husband V i: What a mortal poor Devil is a Husband!
[UK]Bridges Burlesque Homer (3rd edn) 258: But you, with all this hubble-bubble, / Have had a mortal deal of trouble.
[UK]Lytton Paul Clifford III 233: I takes a mortal hinterest in that ’ere chap!
[UK]Comic Almanack Mar. 219: I was in a mortal fright.
[UK]Sam Sly 21 Apr. 4/1: We advise M—l St—ch—e not to have so many mortal sprees at the Fleece Inn.
[UK]T. Buckley Sydenham Greenfinch 11: Tom proceeded to designate Exeter Hall as a ‘mortal cock and hen shop’.
[US]H.L. Williams Darkey Sleep-Walker 3: Mass’ ginerally brushes up some mortal terror for us.
[UK]G.M. Fenn Sappers and Miners 41: I seem to see young Jollivet there going head first over the cliff; and the mortal shiver it did send through me was something as I never felt afore.
[Aus]P. White Tree of Man (1956) 58: I go in mortal terror meself whenever I have the wind.
[NZ]B. Crump Hang On a Minute, Mate (1963) 28: On my way out with a boxful of crockery I dropped it and the wife let out a mortal scream. She thought her time had come.
[US]H. Gould Fort Apache, The Bronx 85: In some quarters it’s considered a mortal insult.

3. long and tedious.

[UK]W. Scott Monastery (1858) 210: The interior one,formed of oak, occupied them for three mortal hours .
[UK]Dickens Oliver Twist (1966) 184: He had not touched a drop of anything for forty-two mortal long hard-working days.
[US]J.M. Field Drama in Pokerville 73: ‘Prehaps,’ Parson Hyme didn’t put it into Pokerville for two mortal hours.
R.L. Stevenson Inland Voyage 255: They performed a piece... in five mortal acts [F&H].
[Aus]H. Lawson ‘On the Edge of a Plane’ in Roderick (1972) 134: The old woman wouldn’t let go my hand for three mortal hours.
[US]‘Hugh McHugh’ Down the Line 59: It took me three mortal hours to convince her that Tom was only talking about a horse.
[Ire]Joyce ‘The Dead’ Dubliners (1956) 174: They forget that my wife here takes three mortal hours to dress herself.
[US]K. Cook Wake in Fright [ebook] Damn it all! He couldn’t just walk up and down the street for six mortal week.

In compounds

mortal lock (n.) (also mortal cinch) [lock n.1 ]

(US, orig. gambling) a certainty, a cinch, esp. of a racehorse, a race or a winning hand in cards.

[US]D. Maurer in Lang. of Und. (1981) 218: Lock or mortal lock...a race to be won easily by a certain horse....A ‘sure thing’ bet....By implication, a fixed race .
[US]Chicago Sun. Trib. 13 Aug. II 6: Mortal Lock [a racehorse] Repeats in Fair Stake [HDAS].
[US]W.S. Hoffman Loser 26: ‘You got something tonight?’ ‘True Duane. Ninth race. He's a mortal cinch’.
[US]W. Murray Tip on a Dead Crab 79: ‘It’s what we used to call a mortal lock.’ [...] ‘An animal that cannot lose the race,’ Sam said. ‘Of which there ain’t any such animals.’.
[US]D. Jenkins Franchise Babe 106: ‘My mortal lock was Nebraska over Alabama in the Orange Bowl’.