Green’s Dictionary of Slang

1. a mess; usu. in phr. make a mull of, make a mess of.

1821		‘An Amateur’ Real Life in London I 606: Somebody must make a mull* — but Randall’s the man — he is the favourite of the day, all the world to a penny roll. [* Mull — Defeat, loss, or disappointment].
1838		Dickens Oliver Twist (1966) 350: Keeping out of the way arter that precious mull that you got me into, which might have cost me my neck.
1849		Era (London) 3 June 3/4: I won’t go no further, in case I should make a mull on it (perhaps I have already).
1854		F. Smedley Harry Coverdale’s Courtship 105: He’d made a regular mull of it.
1860		T. Binney Light & Shadow Appendix No. viii 59: They really cannot themselves tell what the doctrine of the church actually is, although they speak of it as declared! The whole thing is a mull .
1865		R.S. Surtees Facey Romford’s Hounds 186: He was very uncomfortable, and felt he was making a mull of it.
1873		J. Hatton Clytie in Gentleman’s Mag. No. 235 720: And look what a mull you made of the old Earl business!
1887		W.S. Gilbert ‘Phrenology’ Fifty ‘Bab’ Ballads 276: I must have made a mull, / This matter I’ve been blind in it.

2. (also mullah) a simpleton, a clumsy person; thus a country person.

1848		Sam Sly 30 Dec. 4/1: [H]e has just taken from a ‘mull,’ surmounted by a real genuine cairngorm, a pinch of Irish blackguard, with which he is enthusiastically fraternising.
1984		Partridge DSUE (8th edn) 765/2: from ca. 1865.
1996		P. Howard The Joy (2015) [ebook] I promised to beat the shite out of every mullah bastard that ever darkened the door of The Joy.

3. (Aus. drugs) marijuana, esp. when prepared (cleaned, sieved) for smoking.

1985		R.G. Barrett You Wouldn’t Be Dead for Quids (1989) 44: The one holding the bowl dropped it and the mull went all over the floor.
1987		Tracks (Aus.) Dec. 23/4: They said if I didn’t smoke their two ounces of heavy-duty mull, man, then they’d kill ... er ... they’d kill you, Boss!
1996		L. Jaivin Rock n Roll Babes from Outer Space 124: Tristram pinched some mull between his fingers and examined it closely.
2002		S. Maloney Something Fishy (2006) 106: Shit, pot, hemp, grass, weed, ganja, mull. Marijuana.
2012		A. Savage ‘Killing Peacocks’ in Crime Factory: Hard Labour [ebook] Adding under his breath that he grew the best mull in Gippsland.