Green’s Dictionary of Slang

nutter n.

1. a lunatic, an eccentric [nut n.2 (1)].

[UK]F. Norman Bang To Rights 36: The reason for this is to find out wether or not you are a nutter.
[UK]B. McGhee Cut and Run (1963) 173: Nobody wants to antagonize a ‘nutter’.
[UK]P. Fordham Inside the Und. 74: Ernie, always remembered as a ‘nutter’.
[Aus]R.G. Barrett Boys from Binjiwunyawunya 188: He’s a nutter [...] He used to go around chopping off people’s fingers with a meat axe.
[Aus]R.G. Barrett Mud Crab Boogie (2013) [ebook] Sooner or later he’ll pull that caper with a real nutter and wake up the next day in hospital.
[UK]G. Burn Happy Like Murderers 326: Fuck off, you nutter! Fuck off out of it.
[Aus]M.B. ‘Chopper’ Read Chopper 4 142: I put together a crew of nutters never before seen in any prison.
[UK]R. Milward Apples (2023) 68: I watched kids, workers and nutters walking.
[UK]K. Richards Life 26: They were a bit more upper-class nutters - they got wheelchairs or something.
[Scot]I. Welsh Decent Ride 107: Ah’m hopin now that Sal’s no nutter wi a saviour complex.
[Aus]G. Gilmore Base Nature [ebook] ‘Davie, you nutter, that’s the only way to be successful’.
[Aus]P. Papathanasiou Stoning 92: ‘[T]hose religious nutters at the tourist park have a point’.
Twitter 30 Nov. 🌐 The anti-mask nutters are getting their message in now.

2. the head [nut n.1 (1b)].

[UK]N. Dunn Up the Junction 20: So would I. Do me nutter in.

In compounds

nutter butter (n.) [redup.; note brandname Nutter Butter, a form of peanut-filled biscuit]

(US campus) someone who is eccentric or absent-minded.

[US]Eble Sl. and Sociability 42: Examples of rhyme from college slang are [...] nutter butter ‘someone who is unaware or inattentive’.
nutter’s medo (n.)

(N.Z. prison) a tablet of largactil.

[NZ]D. Looser Boobslang [U. Canterbury D.Phil. thesis] 127/1: nutter’s medo n. largactil, a largactil pill.