Okay, I seem to recall seeing such a thing, but can't remember where. Does anyone have any images of wide-bladed daggers other than the late cinqueda? I'm thinking specifically of those with, for lack of a better terminology, a type XIV or XV blade that starts out wide and tapers sharply to the point.[/img]

There were plenty of these in the Bronze and early Iron Age; for example, the Roman pugio. It's a very good design especially for weaker materials like bronze, mating a sturdy blade with a nonetheless sharp point.

There's also the "anelace" which is defined as "a broad dagger formerly worn at the girdle" on dictionary.com. The term appears in the Alliterative Morte Arthure: "But Arthur with an anlace egerly smites." I've been trying to find some pictures of originals, because all I've ever seen is the reproduction offered by MRL (which I think was recently discontinued). But if the MRL version is an at all accurate representation, it seems like the sort of weapon you're looking for.

The Franklin in Chaucer's Canterbury Tales also bears an "anlaas" in his belt.