The Collaborative International Dictionary of English v.0.48:

Phlegmatic \Phleg*mat"ic\, a. [L. phlegmaticus, Gr. ?: cf. F.
   phlegmatique.]
   1. Watery. [Obs.] "Aqueous and phlegmatic." --Sir I. Newton.
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   2. Abounding in phlegm; as, phlegmatic humors; a phlegmatic
      constitution. --Harvey.
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   3. Generating or causing phlegm. "Cold and phlegmatic
      habitations." --Sir T. Browne.
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   4. Not easily excited to action or passion; cold; dull;
      sluggish; heavy; as, a phlegmatic person. --Addison.
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   Phlegmatic temperament (Old Physiol.), lymphatic
      temperament. See under Lymphatic.
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WordNet (r) 3.0 (2006):

phlegmatic
    adj 1: showing little emotion; "a phlegmatic...and certainly
           undemonstrative man" [syn: phlegmatic, phlegmatical]