Scott holding a claymore
A claymore was a Scottish sword.
In 2268, Chief Engineer Montgomery Scott was dazzled by a claymore when all the weapons in the USS Enterprise's armory were replaced by antique weaponry. (TOS: "Day of the Dove") The sword later seen on a shelf in his quarters. (TOS: "By Any Other Name")
The Star Trek Concordance points out that "Scotty appropriates one beautiful sword, thinking it to be an ancient Scottish claymore. He may never have seen one, however – the sword is a cutlass." The concordance is incorrect as the sword was a basket-hilted broadsword, often also referred to as a claymore. [1]
According to the Star Trek Encyclopedia, 4th ed., vol. 1, p. 146, the claymore was being used by Scottish Highlanders in the 16th century. This same source described the claymore as a two-handed sword with a double-edged blade.
There are actually two types of claymore, both Scottish. One type was the large two handed one as seen in the movie "Braveheart"; the second was a 17th Century type as seen in TOS: "Day of the Dove".