Green’s Dictionary of Slang

very well, excellently.

1754		G. Stevens ‘A Cant Song’ Muses Delight 177: The brimstone she wheedled so bienly.
c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Bienly excellently from bien French. She wheedled so bienly. She coaxed or flattered so cleverly.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (3rd edn).
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1861		Vanity Fair (N.Y.) 9 Nov. 216: Else quick I’d cross and bienly dub the jigger.
1881		Trumble Sl. Dict. (1890).