Green’s Dictionary of Slang

nitto! excl.

stop it!

1959		F. Norman Fings I i: Nito. (The cards are hurriedly hidden).
1959		J. Gosling Ghost Squad 25: Thieves’ argot, spoken properly, is a foreign language which needs to be learned [...] ‘nitto’ means ‘stop’ or ‘Be quiet’.
1959		‘The Pickpocket’ in Encounter n.d. in Norman Norman’s London (1969) 66: Nitto, nark it, stoppo, / That’s wot the whizz mob are saying, / Take yer fork from his outer, he’s piping, / If yer banged then yer in fer a striping.
1979		F. Norman Too Many Crooks Spoil the Caper 170: Nito chaps, ’ere comes der filff!
1984		Partridge DSUE (8th edn) 795/1: since ca. 1940.
2011		J.J. Connolly Viva La Madness 373: ‘But you’ve killed people, right?’ [...] ‘Nitto, Roy...’.