Green’s Dictionary of Slang

stiff adv.

1. to a great (and unpleasant) extent.

[UK]Swell’s Night Guide 65: ‘We charges a win for them slums, and a brown for the pawney.’ ‘Oh, that’s coming it stiff [...] Vy, thunder my posh.’.
[US] ‘Billy Vite’ in Jolly Comic Songster 192: She fell stiff stone dead underneath the table.
[Aus]Bulletin (Sydney) 28 Feb. 10/2: ‘By Jove, old man, you must have walked into the nectar divine pretty stiff last night! How much did you score on your own account?’ ‘Seven bottles.’.
[UK]Sporting Times 29 Mar. 2/4: The North-American Indian (I have reason to know) can mix it uncommonly stiff.
[US]A.H. Lewis Boss 272: He hits up th’ bottle pretty stiff.
[US]F. Packard Adventures of Jimmie Dale (1918) I ii: You’re going to get it pretty stiff, anyhow.
[US]A. King Mine Enemy Grows Older (1959) 77: I’m worried stiff.
[UK]R. Hauser Homosexual Society 91: I was frightened stiff in case he would talk and give a description.
[US]‘Red’ Rudensky Gonif 76: We’re going to knock over a bank so stiff it’ll never get up.
[UK](con. 1940s) J. Wolveridge Ain’t it Grand 79: They were worried stiff.

2. (Aus.) in a deliberately uncompetitive manner.

[Aus]Dead Bird (Sydney) 27 July 8/4: ‘C—t, ain’t he a beauty. I say, vot price him on a horse vot y’vanted to run stiff’.
[Aus]Truth (Sydney) 24 Mar. 5/2: Running ‘Stiff’. One witness [...] made the astounding admission that horses were frequently run ‘stiff’ at Randwick, adding that he had done it himself.