The Collaborative International Dictionary of English v.0.48:

Phlegmon \Phleg"mon\, n. [L. phlegmone, phlegmon, inflammation
   beneath the skin, Gr. flegmonh`, fr. fle`gein to burn: cf. F.
   phlegmon.] (Med.)
   Purulent inflammation of the cellular or areolar tissue.
   [1913 Webster]