The Collaborative International Dictionary of English v.0.48:

Rheum \Rhe"um\ (r[=e]"[u^]m), n. [NL., from L. Rha the river
   Volga, on the banks of which it grows. See Rhubarb.] (Bot.)
   A genus of plants. See Rhubarb.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rheum \Rheum\ (r[udd]m), n. [OF. reume, rheume, F. rhume a
   cold,, L. rheuma rheum, from Gr. ???, fr. "rei^n to flow,
   akin to E. stream. See Stream, n., and cf. Hemorrhoids.]
   (Med.)
   A serous or mucous discharge, especially one from the eves or
   nose.
   [1913 Webster]

         I have a rheum in mine eyes too.         --Shak.
   [1913 Webster]

   Salt rheum. (Med.) See Salt rheum, in the Vocabulary.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rhubarb \Rhu"barb\, n. [F. rhubarbe, OF. rubarbe, rheubarbe,
   reubarbare, reobarbe, LL. rheubarbarum for rheum barbarum,
   Gr. ??? (and ??) rhubarb, from the river Rha (the Volga) on
   whose banks it grew. Originally, therefore, it was the
   barbarian plant from the Rha. Cf. Barbarous,
   Rhaponticine.]
   1. (Bot.) The name of several large perennial herbs of the
      genus Rheum and order Polygonaceae.
      [1913 Webster]

   2. The large and fleshy leafstalks of Rheum Rhaponticum and
      other species of the same genus. They are pleasantly acid,
      and are used in cookery. Called also pieplant.
      [1913 Webster]

   3. (Med.) The root of several species of Rheum, used much
      as a cathartic medicine.
      [1913 Webster]

   Monk's rhubarb. (Bot.) See under Monk.

   Turkey rhubarb (Med.), the roots of Rheum Emodi.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rheum
    n 1: a watery discharge from the mucous membranes (especially
         from the eyes or nose)
    2: rhubarb [syn: Rheum, genus Rheum]

Moby Thesaurus II by Grady Ward, 1.0:

179 Moby Thesaurus words for "rheum":
   Asiatic flu, Hong Kong flu, abscess, acute bronchitis, adenoiditis,
   ague, aluminosis, amygdalitis, anemia, ankylosis, anoxia,
   anthracosilicosis, anthracosis, apnea, asbestosis, asphyxiation,
   asthma, ataxia, atrophy, atypical pneumonia, autacoid, backache,
   bile, bituminosis, black lung, bleeding, blennorhea,
   bronchial pneumonia, bronchiectasis, bronchiolitis, bronchitis,
   bronchopneumonia, cachexia, cachexy, catarrh, chalicosis, chalone,
   chill, chills, chronic bronchitis, chyle, cold, colic,
   collapsed lung, colostrum, common cold, coniosis, constipation,
   convulsion, coryza, coughing, croup, croupous pneumonia, cyanosis,
   diarrhea, digestive secretion, discharge, dizziness,
   double pneumonia, dropsy, dry pleurisy, dysentery, dyspepsia,
   dyspnea, edema, emaciation, emphysema, empyema, endocrine,
   epidemic pleurodynia, fainting, fatigue, fever, fibrillation,
   fibrinous pneumonia, flu, flux, gall, gastric juice, gleet, grippe,
   growth, hay fever, hemorrhage, high blood pressure, hormone, humor,
   hydrops, hypertension, hypotension, ichor, icterus, indigestion,
   inflammation, influenza, insomnia, intestinal juice, itching,
   jaundice, la grippe, labored breathing, lachryma, lactation,
   laryngitis, leukorrhea, lipoid pneumonia, lobar pneumonia,
   low blood pressure, lumbago, lung cancer, lung fever, lymph,
   marasmus, matter, milk, mucor, mucus, nasal discharge, nausea,
   necrosis, pain, pancreatic juice, paralysis, peccant humor,
   pharyngitis, phlegm, pleurisy, pleuritis, pneumococcal pneumonia,
   pneumoconiosis, pneumonia, pneumonic fever, pneumothorax,
   prostatic fluid, pruritus, purulence, pus, quinsy, rash, saliva,
   salivary secretion, sanies, sclerosis, seizure, semen,
   serous fluid, serum, shock, siderosis, silicosis, skin eruption,
   sneezing, snot, sore, sore throat, spasm, sperm, suppuration,
   sweat, swine flu, tabes, tachycardia, tear, teardrop, tears,
   the sniffles, the snuffles, the whites, thyroxin, tonsilitis,
   tumor, upset stomach, urine, vertigo, virus pneumonia, vomiting,
   wasting, wet pleurisy, whooping cough