Meaning: a shortened form of Dionysios, from Dionysus, the name of the Greek god of wine, revelry, fertility and madness, composed of Greek Dios meaning "of Zeus" combined with Nysa, the name of the region where the god Dionysus was raised, possibly meaning "tree" though the etymology is uncertain. However, Dionysus is believed to be pre-Greek, possibly Thracian in origin.
It could also just be its own form meaning "of Zeus".
In Greek mythology, Dion was a king of Laconia who, with his wife Amphithea, had 3 daughters: Orphe, Lyco, and Carya (or Karya). The god Apollo, who had received great hospitality from them, decided to bestow Dion's daughters with the gift of prophecy on the condition that they never betray the gods. However, when the god Dionysus fell in love with Carya, her sisters tried to prevent the liasion, which ended up with them being turned into rocks and Carya into a walnut tree.