The Collaborative International Dictionary of English v.0.48:

Papyrus \Pa*py"rus\, n.; pl. Papyri. [L., fr. Gr. pa`pyros.
   See Paper.]
   1. (Bot.) A tall rushlike plant (Cyperus Papyrus) of the
      Sedge family, formerly growing in Egypt, and now found in
      Abyssinia, Syria, Sicily, etc. The stem is triangular and
      about an inch thick.
      [1913 Webster]

   2. The material upon which the ancient Egyptians wrote. It
      was formed by cutting the stem of the plant into thin
      longitudinal slices, which were gummed together and
      pressed.
      [1913 Webster]

   3. A manuscript written on papyrus; esp., pl., written
      scrolls made of papyrus; as, the papyri of Egypt or
      Herculaneum.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Cyperus papyrus
    n 1: tall sedge of the Nile valley yielding fiber that served
         many purposes in historic times [syn: papyrus, Egyptian
         paper reed, Egyptian paper rush, paper rush, paper
         plant, Cyperus papyrus]