Superstition was a belief system.
Before the Intuitive Revelation, Gallifrey was a matriarchal society ruled by the Pythia through magic and superstition. After the Revelation, it became patriarchal and promoted reason and science. (PROSE: Cat's Cradle: Time's Crucible)
The Architect was known to have been a Devotee of Apeiron though knowledge of this was kept secret amongst the Gallifreyans due to the superstition involved with being associated with such a cult at the time. (PROSE: The Ancestor Cell)