(Greek mythology) a maiden seduced by Zeus; when Hera was about to discover them together Zeus turned her into a white heifer
the closest of Jupiter's moons; has active volcanoes
- At once he slew him and set Io free.
- Better that she should have resumed her former shape, as I permitted Io to do.
- She sent a gadfly to torment Io, who, in her flight, swam through the sea, named after her, Ionian.