Green’s Dictionary of Slang

(Aus.) in an illegal or underhand manner.

1903		J. Furphy Such Is Life n.p.: Toby was to get a note if he won the big event, and nothing if he lost; but it paid us to give him two notes to run cronk.
1906		H. Lawson When I Was King n.p.: I’ve been a fool, but such is fate - / I guess I’ll talk the guv’nor round: / ‘I’ve acted cronk,’ I’ll tell him straight; / (He’s had his time too, I’ll be bound).
1913		Truth (Sydney) 17 Aug. 11/4: Giving coppers information / As they pick up cronk, of course.
1948		J. Furphy Buln-Buln and the Brolga n.p.: In fact, I have formulated a science, which I call Nomenology, and which, like all other sciences except Mathematics, sometimes runs cronk .