Green’s Dictionary of Slang

(Aus./US) a fool; a lunatic.

1902		Bulletin (Sydney) 23 Aug. 20/4: Rev. Silly-Dilly Macky sees a great danger to the cause of the Yellow Pup in N.S.W. in Womanhood Suffrage, as the R.C. woman ‘will vote as their priests tell them to.’ Thus [...] Popish dominance is threatened!
1910		Bulletin (Sydney) 21 July 10/4: Inquiry concerning Whiskers demonstrated that nobody knew whose madman he was, and none could tell why he was in, or how, or anything concerning him. In this extremity the uncertified dilly was called before Authority.
1918		‘Lance Corporal Cobber’ Anzac Pilgrim’s Progress 34: We know, for we’re no dillys on guff and guvyer fed.
1942		N. Algren Never Come Morning (1988) 112: The guy’s a dilly [...] He’s forgot what he’s here for.
1955		R. Graziano Somebody Up There Likes Me (1956) 102: Every time I was up for a new cellmate they [...] give me a real dilly.
1962		S. Longstreet Flesh Peddlers (1964) 259: The dillies with the cuffedpants.
1970		in P.R. Runkel Law Unto Themselves 27: What a dilly he is – the Captain we got is haircut nutty.
1976		R. Carver Stories (1985) 339: ‘Oh, he have himself a dilly of a headache’.