Because of the length, this sounds like a large dagger. Dirk and stiletto always both stick in my mind as longer, narrower blades meant for plunging. However, with a slightly longer blade of the same width, one could make a legitimate claim that one’s “dagger” is really a “main gauche” (French for “left hand”), which is one’s parrying, finishing, and last-resort weapon in two-handed swordfighting.
I think the deciding factor is a combination of blade width and the blade’s width-to-length ratio. If it’s a skinny blade, it doesn’t really become a short sword until it’s the size of a decent main gauche; if it’s a fat blade, it could be considered a short sword around machete length or shorter.
And of course, if you’re holding it, you get to decide.