Green’s Dictionary of Slang

1. an informer.

c.1698		B.E. Dict. Canting Crew n.p.: Whiddler, a Peacher (or rather Impeacher) of his Gang.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
a.1790		H.T. Potter New Dict. Cant (1795).
1809		G. Andrewes Dict. Sl. and Cant.
1811		Lex. Balatronicum.
1812		Vaux Vocab. of the Flash Lang.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1835		G. Kent Modern Flash Dict. 35: Whiddler [...] an informer.
1848		Flash Dict. in Sinks of London Laid Open [as cit. 1835].
1859		Matsell Vocabulum.

2. a talkative individual.

a.1790		H.T. Potter New Dict. Cant (1795) n.p.: whiddler talkative fellow.
1809		G. Andrewes Dict. Sl. and Cant.
1812		Vaux Vocab. of the Flash Lang. in McLachlan (1964) 279: whiddler a talkative or tell-tale person, who is not fit to be trusted with a secret.
1835		G. Kent Modern Flash Dict. 35: Whiddler – a talkative fellow.
1848		Flash Dict. in Sinks of London Laid Open [as cit. 1835].

3. see Whiddler n.