Stephenson:Neal:Quicksilver:3:Jack Ketch (Neal Stephenson)
From the Quicksilver Metaweb.
A general-purpose moniker applied to any executioner.
The manor of Tyburn was formerly held by Richard Jaquett, where felons for a long time were executed; from whence we have Jack Ketch. - Lloyd's MS., British Museum.
This is somewhat anachronistic.
(see also: Stephenson:Neal:Quicksilver:343:Jack Ketch (The Shabby Sheik))