A little blade

[Marcus den toom]

Without any expertise on these knifes i would say this is a tool used in a barn or shed and hung from that mysterious hole via a nail?

But than again it might just very well be the letter opener that was used in the famous letter from Napoleon when he was defeated?

[Jim McDougall]

While this blade seems highly indicative of a dagger, as Fernando notes, there are hunting knives with central ridge (mostly I think with various stag horn etc. hilts) and I would think that curious aperture is likely more for a rivet or hilt securing than any practical purpose.
The patination does indeed suggest age which could certainly be 19th c.

[fernando]

Thank you Jim.
A bit distant from the tang for hilt securing, don't you think ?

[Jim McDougall]

Originally Posted by fernando

Thank you Jim.
A bit distant from the tang for hilt securing, don't you think ?

Probably so, but who knows what the hilt was like. Sounded logical but then maybe it is just for hanging it on a wall, like the ruler there