Green’s Dictionary of Slang

(UK Und.) a bribe, a ‘sweetener’; one who takes money with false promises.

1777		Norfolk Chron. 8 Feb. 2/3: A certain gentleman [...] has accepted a trifling doucer of 12,000 guineas, rather than be at the trouble of going through a legal process.
[1781		G. Parker View of Society II 19: A douceur properly applied has worked miracles. In such a case, secrecy must not only be promised, but inevitable preserved. However, even there, the douceur ought not to precede the employment].
1782		Stamford Mercury 3 Jan. 2/3: The possessor was obliged [...] to give a doucer of 100l. to prevent a foreclosure.
1810		Morn. Chron. 18 Aug. 3/2: For this agency he received a considerable doucer.
1832		Huntingdon, Bedford & Peterborough Gaz. 31 Mar. 2/3: The upper servants [...] actually claim a doucer of 3s. a chaldron for themselves.
1847		Elgin Courier 23 Apr. 2/2: Paddy [...] said that if the promised doucer was handed over he would give the required information.
1850		Dundee, Perth & Cupar Advertiser 29 Jan. 1/5: It was agreed [...] that the doucer of 110l. would be paid upon an appointment of 110l. being procured.
1865		Leaves from Diary of Celebrated Burglar 86/1: Finally we both concluded that it was best to ‘sweeten’ the ‘cops’ by ‘slinging’ an occasional ‘doucer,’ and purchase their absence from the ‘drum’.
1872		Cheshire Obs. 3 Feb. 5/6: Each would be accompanied by a doucer to esnure it a good position, which would be allotted according to the amount given.
1880		R. Rowe Picked Up in the Streets 132: Jack, half-muddled with the beer on which he had spent his copper doucers.
1888		Sheffield Eve. Teleg. 25 Jan. 4/4: Sir Morell has just refused a nice little doucer on [sic] 30,000 dollars, which was offered to him if he would run across the ‘mill-pond’ to see one of the inumerable ‘leading citizens’ in the Staes .
1906		A. McCormick Tinkler-Gypsies of Galloway 279: Billy accepts a Doucer.