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):

papyrus
    n 1: paper made from the papyrus plant by cutting it in strips
         and pressing it flat; used by ancient Egyptians and Greeks
         and Romans
    2: 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]
    3: a document written on papyrus