The Collaborative International Dictionary of English v.0.48:

Phlegm \Phlegm\ (fl[e^]m), n. [F. phlegme, flegme, L. phlegma,
   fr. Gr. fle`gma a flame, inflammation, phlegm, a morbid,
   clammy humor in the body, fr. fle`gein 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.
      [1913 Webster]

   2. (Physiol.) Viscid mucus secreted in abnormal quantity in
      the respiratory and digestive passages.
      [1913 Webster]

   3. (Old Chem.) A watery distilled liquor, in distinction from
      a spirituous liquor. --Crabb.
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   4. Sluggishness of temperament; dullness; want of interest;
      indifference; coldness.
      [1913 Webster]

            They judge with fury, but they write with phlegm.
                                                  --Pope.
      [1913 Webster]

WordNet (r) 3.0 (2006):

phlegm
    n 1: apathy demonstrated by an absence of emotional reactions
         [syn: emotionlessness, impassivity, impassiveness,
         phlegm, 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: phlegm, sputum]
    3: inactivity; showing an unusual lack of energy; "the general
       appearance of sluggishness alarmed his friends" [syn:
       languor, lethargy, sluggishness, phlegm, flatness]