1749, "two-edged broadsword of ancient Scottish Highlanders," from Gaelic claidheamh mor "great sword," from claidheb "sword" (cf. Welsh cleddyf), possibly from PIE root *kel- "to strike" (see holt) + mor "great" (cf. Welsh mawr; see more). An antiquarian word made familiar again by Scott's novels; modern military application to pellet-scattering anti-personnel mine is first attested 1962.
A danger; an unpredicted peril: skipping from television to a feature-film career has its built-in Claymore
[1990s+; fr the US claymore antipersonnel mine, named in turn for a Scottish broadsword]