borrowed from Greek, combining form from mélās, stem melan- (feminine mélaina, neuter mélan) "dark-colored, black," perhaps from Indo-European *mel-h2-n-, whence also Latvian mȩl̃ns "black," Old Prussian melne "blue spot," and, without -n- and with lengthened grade, Lithuanian mė́las, mė́lynas "blue"
Note: Associated more indefinitely with a host of other words with the frame m-l-, as Sanskrit mala- "dirt," Germanic *mēla- "spot, mark" (see mole entry 1). In Greek the combining form has an athematic variant melan-, as in melancholía melancholy entry 1.