The Collaborative International Dictionary of English v.0.48:

Plectrum \Plec"trum\, n.; pl. L. Plectra, E. Plectrums . [L.,
   fr. Gr. ? anything to strike with, fr.? to strike.]
   A small instrument of ivory, wood, metal, or quill, used in
   playing upon the lyre and other stringed instruments.
   [1913 Webster]