The name Medusa brings about bad images.
A few others:
ACACIA f English From the name of a type of tree, ultimately deriving from Greek ακη (ake) "thorn, point".
BIFF m English From a nickname which was based on the English word biff, which means "punch, hit, strike".
BLAKE m English From a surname which meant either "black" or "pale" in Old English. A famous bearer of the surname was the poet and artist William Blake.
ANGRA MAINYU m Near Eastern Mythology Means "evil spirit" in Avestan. In Persian mythology Angra Mainyu was the god of darkness, death and destruction, the enemy of Ahura Mazda.
AZAZEL m Biblical Hebrew Means "scapegoat" in Hebrew. This is the name of the recipient of a sacrificial goat in the Old Testament. The identity of Azazel is not clear; it may in fact be the name of the place where the goat is to be sacrificed, or it may be the name of some sort of evil desert demon.
CHERNOBOG m Slavic Mythology Means "the black god" from Slavic cherno "black" and bog "god". Chernobog was the Slavic god of darkness, evil and grief.
LOKI m Norse Mythology Meaning unknown, possibly derived from the Indo-European root *leug meaning "to break". In Norse legend Loki was a trickster god associated with magic and fire. Over time he became more and more evil, and he was eventually chained to a rock by the other gods.