Empusa (Ancient Greek: Ἔμπουσα, Empousa, of unknown meaning) is a demigoddess of Greek mythology. In later incarnations she appeared as a species of monsters commanded by Hecate (known in English as an empuse).
She is often associated or grouped with the demigoddesses Lamia and Mormo, who were likewise related as a kind of spectres in later mythology (the lamias and mormolyceas, respectively).
Empusa was the beautiful daughter of the goddess Hecate and the spirit Mormo. She feasted on blood by seducing young men as they slept (see sleep paralysis), before drinking their blood and eating their flesh. When she spotted a man sleeping on the road, she attacked him, little knowing he was Zeus, king of the gods. Zeus woke and visited his wrath on her and Empusa was killed. Empusa is pictured as wearing brazen slippers and bearing flaming hair. By folk etymology, her name was said to mean "one-footed" (from Greek *έμπούς, *empous: en-, one + pous, foot). This gave rise to the iconography of a one-legged hybrid, with a donkey's leg and a brass prosthetic leg.
In later Greek mythology, her role was reduced to a species of spectre called an empuse or empusa (pl. empusae). The empusae were sent by Hecate to guard roads and devour travelers (Hecate was also the goddess of roadsides). According to Philostratus, empusae ran and hid, uttering a high-pitched scream, at the sound of insults. The empusae are best known for their appearance in Aristophanes's The Frogs, in which they scared Dionysus and Xanthias on their way to the underworld.