The Collaborative International Dictionary of English v.0.48:

Languor \Lan"guor\, n. [OE. langour, OF. langour, F. langueur,
   L. languor. See Languish.]
   1. A state of the body or mind which is caused by exhaustion
      of strength and characterized by a languid feeling;
      feebleness; lassitude; laxity.
      [1913 Webster]

   2. Any enfeebling disease. [Obs.]
      [1913 Webster]

            Sick men with divers languors.        --Wyclif (Luke
                                                  iv. 40).
      [1913 Webster]

   3. Listless indolence; dreaminess. --Pope. " German dreams,
      Italian languors." --The Century.

   Syn: Feebleness; weakness; faintness; weariness; dullness;
        heaviness; lassitude; listlessness.
        [1913 Webster]

WordNet (r) 3.0 (2006):

languor
    n 1: a relaxed comfortable feeling [syn: languor,
         dreaminess]
    2: a feeling of lack of interest or energy [syn: languor,
       lassitude, listlessness]
    3: inactivity; showing an unusual lack of energy; "the general
       appearance of sluggishness alarmed his friends" [syn:
       languor, lethargy, sluggishness, phlegm, flatness]

Moby Thesaurus II by Grady Ward, 1.0:

126 Moby Thesaurus words for "languor":
   abeyance, acedia, adynamia, anemia, apathy, atony, blah feeling,
   bloodlessness, blues, boredom, brain fag, cachexia, cachexy,
   catalepsy, catatonia, cautiousness, circumspection, coma,
   cowardice, creeping, deadliness, deathliness, debilitation,
   debility, deliberateness, deliberation, depression, doldrums,
   dormancy, doziness, drawl, drowsiness, dullness, dumps, enervation,
   enfeeblement, ennui, entropy, etiolation, exhaustion, eyestrain,
   faintness, fatigue, feebleness, flabbiness, flaccidity,
   foot-dragging, goneness, heart strain, heaviness, hebetude,
   idleness, impotence, inanimation, indifference, indolence, inertia,
   inertness, jadedness, lackadaisicalness, languidness, languishment,
   languorousness, lassitude, latency, laziness, leisureliness,
   lenitude, lentitude, lentor, lethargy, lifelessness, listlessness,
   lotus-eating, mental fatigue, mental strain, oscitancy, oscitation,
   overstrain, overtiredness, pandiculation, passiveness, passivity,
   phlegm, pokiness, prostration, reluctance, satedness, slackness,
   sleep, sleepiness, sloth, slothfulness, slowness, sluggardy,
   sluggishness, slumber, softness, somnolence, somnolency, stagnancy,
   stagnation, stance fatigue, stasis, strain, strengthlessness,
   stretching, stupefaction, stupor, supineness, suspense, tedium,
   tentativeness, tiredness, torpidity, torpidness, torpitude, torpor,
   vegetation, vis inertiae, weakliness, weakness, wearifulness,
   weariness, world-weariness, yawning