The Collaborative International Dictionary of English v.0.48:

Charpie \Char"pie\, n. [F., properly fem. p. p. of OF. charpir,
   carpir, to pluck, fr. L. carpere. Cf. Carpet.] (Med.)
   Straight threads obtained by unraveling old linen cloth; --
   used for surgical dressings.
   [1913 Webster]