Green’s Dictionary of Slang

dilly adj.¹

1. foolish.

[1799		Sporting Mag. Apr. XIV 31/1: [heading] Letter of a Fribble to a Friend. [...] I am, Sir, Your very humble servant, Dilly Dimple].
[1873		Williams & Jones Gloss. Somersetshire 11: Dilly, [...] cranky, queer].
1906		E. Dyson Fact’ry ’Ands 234: Ellis [...] be ther dilly nature iv him, got himself yanked up ’tween belt ’n’ pully.
1915		C.J. Dennis ‘Spring Song’ in Songs of a Sentimental Bloke 16: If this ’ere dilly feelin’ doesn’t stop / l lose me block an’ stoush some flamin’ cop!
1918		Aussie (France) 7 Sept. 7/2: Don’t youse blokes reckon a cove’s dilly to splice one of them mademoiselles when there’s whips of Aussie tarts like these?
1924		C.J. Dennis ‘The Faltering Knight’ in Rose of Spadgers 19: A bloke gets born, [...] / Dreams dilly dreams, then wakes to find a wife.
1935		L.A. Times 24 Mar. II 1/7: DILLY NELL: A recalcitrant or dilatory girl dancer.
1946		Argus (Melbourne) 18 June 4/3: I would be dilly if I didn’t know the public has been swell towards me.
1959		I. & P. Opie Lore and Lang. of Schoolchildren (1977) 201: A ‘dilly-day-dream’.
1960		J. Franklyn Dict. of Rhy. Sl.
1974		(con. 1945) M. Angelou Gather Together In My Name 155: My silly dilly wife stopped letting me have any.

2. mad.

1906		E. Dyson Fact’ry ’Ands 214: Who should come sprintin’ upstairs but me nibs, pale’s er blessed egg, hair on end — fair dilly.
1914		Truth (Melbourne) 10 Jan. 11/3: The ring-siders went fairly dilly when he made his first appearance.
1918		C.J. Dennis ‘Digger Smith’ in Chisholm (1951) 93: Maybe ’e’s dilly. I’ll go down an see.
1956		Argus (Melbourne) 23 Feb. 2/5: [headline][ Dilly Dali.

In compounds

dilly dude (n.) [orig. Ohio use]

(US black) an eccentric, an outsider.

1969

Current Sl. III:3 5: Dilly dude, n. Someone with strange habits; a homosexual; a ‘weirdo.’.