Sinjin’s Wood, n. — Green’s Dictionary of Slang

Sinjin’s Wood n.

[the affectedly smart pron. of St John’s + deliberate puns on the ‘sin’ and ‘gin’ available in St John’s Wood, then an area of London notorious for its kept women and prostitutes]

St John’s Wood.

1863		Beds. Mercury 12 Sept. 3/1: ‘I was takin kare ov a Willow in Sinjin Wood for a famile wot had gone out ov town for the seeson’.
1881		Sporting Times 9 Apr. 3/4: ’Will you be so kind, Mr Blobbs, to inform me when you are going to pay me that little account of twnety-five pounds?’ asked a Sinjin’s Wood tailor.
1879		Examiner (London) 5 July 19/1: Instructions on the pronunciation of St John. When this is a family name you should say Sinjin, but on no account must you talk of Sinjin Church or Sinjin the Baptist.
1909		J. Ware Passing Eng. of the Victorian Era.