Green’s Dictionary of Slang

kadoova n.

the head.

1885

Bulletin (Sydney) 12 Sept. 9/2: If Baradas had a head of hair as represented by Mr. Little, there is no wonder that he was a scoundrel. Any man with his ‘kadoova’ so heavily handicapped would be capable of any crime.

In phrases

off one’s kadoova (adj.)

(Aus.) crazy, eccentric, mentally unstable.

1885		Bulletin (Sydney) 24 Jan. 5/4: Folks said he, too, was of unsound intellect – was ‘off his bloomin’ kadoova’ they called it, just as Richard Dorff was, and we […] worked our rich partner up with whiskey until he amply proved the justice of his critics’ assertions. [Ibid.] 25 Apr. 11/1: We are deluged with returns showing the number of unfortunates who are sent off their kadoova by filling themselves with spirits out of quart bottles, but what we yearn for now is a list of those who are worked equally mad by the spirit ladled out from the pulpit.
1946		D. Stivens Courtship of Uncle Henry 72: I reckoned then Thompson was a bit off his kadoova.
1955		N. Pulliam I Travelled a Lonely Land (1957) 236/2: off your kadoova – you’re ‘batty’, silly.