Fidius
An ancient form of filius, occurs in the connection of Dius Fidius, or Medius Fidius, that is me Dius filius, or the son of Jupiter, that is Hercules. Hence the expression medius fidius is equivalent to me Hercules scil. juvet. Sometimes fidius is used alone.
Some of the ancients connected fidius with fides.
Flaccus, Fulvius. The name of two distinguished families in the Fulvia and Valeria gentes.