A yea-nay sort of a fellow, with no backbone. “Da,” in French, means both oui and nenni, as Oui-da (ay marry), Nenni-da (no forsooth).
“I wish that French brother of his, the Parisian la-de-da, was more like him, more of an American.” —A. G. Gunter: Baron Montez, book iii. 8.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894