plectrum

noun

1. A small piece of plastic, metal, ivory, etc., for plucking the strings of a guitar, lyre, mandolin, etc.

   “For sounds in winter nights, and often in winter days, I heard the forlorn but melodious note of a hooting owl indefinitely far; such a sound as the frozen earth would yield if struck with a suitable plectrum, the very lingua vernacula of Walden Wood, and quite familiar to me at last, though I never saw the bird while it was making it.”

2. A projection of bone or other stiff tissue, such as the ridges in some insects' stridulatory organs.