Terminology
The term claymore is an anglicisation of the Gaelic claidheamh mòr "great sword", first attested in 1772 (as Cly-more) with the gloss "great two-handed sword". The sense "basket-hilted broadsword" is contemporaneous, attested in 1773 as "The broad-sword now used called the Claymore, (i.e. the great sword)." OED observes that the latter usage is "inexact, but very common". The 1911 Encyclopædia Britannica likewise judged that the term is "wrongly" applied to the basket-hilted sword.
Authors arguing that the basket-hilted sword is "incorrectly" called claymore have been known to suggest that claybeg (from a purported Gaelic claidheamh beag "small sword") should be used instead.
This does not parallel Scottish Gaelic usage. According to the Gaelic Dictionary by R. A. Armstrong (1825), claidheamh mòr translates to "broadsword", and claidheamh dà làimh to "two-handed sword", while claidheamh beag is given as a translation of "Bilbo".
The term "claymore" became part of vocabulary of the Victorian era sentimental or Romanticist "retro-Jacobite" literature and poetry such as the Skye Boat Song (1870).
Other contemporary Gaelic descriptives of swords include claidheamh cuil or back sword, referring to a single-edged sword with a flat "spine" (not one worn on the back, a common misinterpretation), the claidheamh crom or crooked sword, which could describe either a typical sabre style blade (such as that worn by Archibald Campbell, 1st Duke of Argyll, in the painting by Medina) or a scimitar style blade known as a "Turcael" ("Turkish" blade) such as that brandished by Alasdair Mor, the Champion of Clan Grant, in the c. 1715 portrait by Waitt, or the claidheamh caol or narrow sword, usually describing a rapier or small-sword.
The term claybeg, purportedly from Scots Gaelic claidheamh beag meaning "little sword" is not seen in clan-era Gaelic song or poetry, 'Dwelly's', or other authorities, and seems to be a fairly recent invention.
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