Um explicação dada na seção de anotações do book *:
How it was that he came by the name of Sweeney . . . there to look for it: the name is indeed an unusual one. The surname Todd or 'tod' [sic], a northern word of unknown origin from Middle English, means, literally, 'fox'; metaphorically it was used to refer to 'a person likened to a fox; a crafty person' (OED). Sweeney or 'sweeny' [sic], although referring literally to atrophy in the shoulder-muscles of a horse, was also more commonly and figuratively used to connote 'the stiffness of "pride" or self-conceit' (OED). Alternatively, Sweeney's name may have recalled for some readers the Irish name and figure of the mad king 'Sweeney' of the Buile Suibhne of Celtic legend. Louis James, in his Fiction for the Working Man (Oxford, 1963), first noted with reference to the story's original title that an interesting process of association of ideas is suggested by the fact that the London Directories record an "S. Todd, pearl-stringer", who lived at Clerkenwell at this time' (191). Finally, the name may simply be an unconsciously reversed recollection and slightly jumbled reformulation, in its assonance, of the character of 'Poll Sweedlepipe' in Dickens's Martin Chuzzlewit (see Introduction, xvii). Sweedlepipe, whose services as 'an easy shaver ... and a fashionable hairdresser, also' were advertised to his clients in his shop-window at Kingsgate Street, High Holborn, would still have been fresh in the public's imagination.
(* Sweeney Todd: O Barbeiro Demoníaco da Fleet Street, EUA e Canadá)