Source : Webster's Revised Unabridged Dictionary (1913)

Phlegm \Phlegm\, n. [F. phlegme, flegme, L. phlegma, fr. Gr. ? a
   flame, inflammation, phlegm, a morbid, clammy humor in the
   body, fr. ? to burn. Cf. {Phlox}, {Flagrant}, {Flame},
   {Bleak}, a., and {Fluminate}.]
   1. One of the four humors of which the ancients supposed the
      blood to be composed. See {Humor}. --Arbuthnot.

   2. (Physiol.) Viscid mucus secreted in abnormal quantity in
      the respiratory and digestive passages.

   3. (Old Chem.) A watery distilled liquor, in distinction from
      a spirituous liquor. --Crabb.

   4. Sluggishness of temperament; dullness; want of interest;
      indifference; coldness.

            They judge with fury, but they write with phlegm.
                                                  --Pope.

Source : WordNet®

phlegm
     n 1: apathy demonstrated by an absence of emotional reactions
          [syn: {emotionlessness}, {impassivity}, {impassiveness},
           {indifference}, {stolidity}, {unemotionality}]
     2: expectorated matter; saliva mixed with discharges from the
        respiratory passages; in ancient and medieval physiology
        it was believed to cause sluggishness [syn: {sputum}]
     3: inactivity; showing an unusual lack of energy [syn: {languor},
         {lethargy}, {sluggishness}]