Green’s Dictionary of Slang

audacity, calmness.

c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Nine Shillings, Corruption of Nonchalance.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn).
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.