Green’s Dictionary of Slang

a willingness to be fooled.

1748–49		Cleland Memoirs of a Woman of Pleasure (1985) 128: There is, in short, in the men, once they are caught, by the eye specially, a kind of cullibility, that their lordly wisdom little dreams of.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Cullability, a disposition liable to be cheated, an unsuspecting nature, open to imposition.
1811		Lex. Balatronicum [as cit. 1785].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.