MORMO
a female spectre, with which the Greeks used to frighten little children. Mormo was one of the same class of bugbears as Empusa and Lamia.
EMPUSA
or Empousa, a monstrous spectre, which was believed to devour human beings. It could assume different forms, and was sent out by Hecate to frighten travellers. It was believed usually to appear with one leg of brass and the other of an ass. Whenever a traveller addressed the monster with insulting words, it used to flee and utter a shrill sound.
The Lamiae and Mormolyceia, who assumed the form of handsome women for the purpose of attracting young men, and then sucked their blood like vampyrs and ate their flesh, were reckoned among the Empusae.
LAMIA
In later times Lamiae were conceived as handsome ghostly women, who by voluptuous artifices attracted young men, in order to enjoy their fresh, youthful, and pure flesh and blood. They were thus in ancient times what the vampires are in modern legends.
[ See: Lamia by John Keats ]
MORMOLYCE or MORMOLYCEION
the same phantom or bugbear as Mormo, and also used for the same purpose.
From The Dictionary of Greek and Roman Biography and Mythology.