My understanding is that the Scots had a "weapon knife," smaller than the cleighmore, or broadsword, but big enough to be called a short-sword by anyone else*. In Scots dialect, then, "weepon knife" and "wee pen-knife" could be homophones when two different blades are meant. So when a "wee penknife" is long and sharp, it's probably not a penknife. When it's an easily concealed blade, it's possibly a penknife that was meant.

Bob Clayton

* A Roman army sword might be a largish weapon knife. A Bowie knife would certainly be more like what the Scotsman would use. I don't know what they call those little knives that go in their socks, though. Perhaps THOSE are also 'weapon knives,' in which case the things come in many sizes.