The Collaborative International Dictionary of English v.0.48:

Mucilage \Mu"ci*lage\, n. [F., from L. mucilago a musty juice,
   fr. mucus mucus, slime. See Mucus.]
   1. (Bot. Chem.) A gummy or gelatinous substance produced in
      certain plants by the action of water on the cell wall, as
      in the seeds of quinces, of flax, etc.
      [1913 Webster]

   2. An aqueous solution of gum, or of substances allied to it;
      a glue; a liquid adhesive; as, medicinal mucilage;
      mucilage for fastening envelopes.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mucilage
    n 1: a gelatinous substance secreted by plants
    2: cement consisting of a sticky substance that is used as an
       adhesive [syn: glue, gum, mucilage]