Merriam-Webster Collegiate Dictionary - phlegm

 noun  Etymology: Middle English fleume, from Anglo-French, from Late Latin ~at-, ~a, from Greek, flame, inflammation, ~, from phlegein to burn — more at black  Date: 13th century  1. the one of the four humors in early physiology that was considered to be cold and moist and to cause sluggishness  2. viscid mucus secreted in abnormal quantity in the respiratory passages  3.  a. dull or apathetic coldness or indifference  b. intrepid coolness or calm fortitude  • ~y adjective