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]

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "mucilage":
   adherent, adhesive, albumen, antifriction, barnacle, batter,
   black lead, bonnyclabber, bramble, brier, bulldog, burr, butter,
   cement, clabber, cornstarch, cream, curd, decal, decalcomania,
   dough, egg white, gaum, gel, gelatin, glair, glop, glue, gluten,
   glycerin, goo, gook, goop, graphite, gruel, gumbo, gunk, jam, jell,
   jelly, leech, limpet, loblolly, lubricant, lubricating oil,
   lubricator, molasses, mucus, pap, paste, plaster, plumbago,
   porridge, prickle, pudding, pulp, puree, putty, remora, rob,
   semifluid, semiliquid, silicone, size, soup, starch, sticker,
   sticky mess, syrup, thorn, treacle, wax