As told in the Devi-Mahatmya, a group of demons (daityas), led by Canda and Munda are fighting Durga.  When Durga becomes angry, Kali leaps forth from her forehead to do battle with the demons.  After defeating the daitya army, Kali takes on first Canda and then Munda, easily dispatching them.  With their two leaders dead, the rest of the armies flee in a panic.  Kali then presents the heads of the two “generals” to their leader, who “graciously” concedes the battles to her, and bestows the name of “Chamunda” upon her.
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http://www.aghori.it/devi_mahatmya.htm