Green’s Dictionary of Slang

the penis, based on sexual intercourse as an agency of peace between married couples.

1708		N. Ward Adam and Eve 109: A loving Reconciliation, by the seasonable Intercession of the Matrimonial Peace-maker.
1733		Laugh and Be Fat 27: He had more Wit in his Anger, than to revenge himself of an ill Tongue, by burning his Peace-maker. [Ibid.] 81: Then tumbled into Bed, where all past Differences were reconcil’d by the matrimonial Peace-Maker.
c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Matrimonial Peace Maker. The Sugar Stick.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.: Matrimonial Peace-maker. The sugarstick, or arbor vitae.
1811		Lex. Balatronicum [as cit. 1788].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue [as cit. 1788].
[1840		‘The Tree of Life’ in Fake Away Songster in Spedding & Watt (eds) Bawdy Songbooks (2011) III 293: It cures all dissentions ’twixt husband and wife / [...] / By a right application it can never fail].
1890–1904		Farmer & Henley Sl. and Its Analogues [as cit. 1788].