Definition of Io in English:


proper noun

  • 1Greek Mythology
    A priestess of Hera who was loved by Zeus. Trying to protect her from the jealousy of Hera, Zeus turned Io into a heifer. Hera sent a gadfly to torture the heifer, which then fled across the world and finally reached Egypt, where Zeus turned her back into human form.

  • 2Astronomy
    One of the Galilean moons of Jupiter, the fifth-closest satellite to the planet, being actively volcanic and coloured red and yellow with sulphur compounds (diameter 3,630 km).