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)
People from the West Country were sometimes characterised as being traditional and somewhat superstitious. (PROSE: The Devil Goblins from Neptune)
Captain Alexander Marfleet inherited a superstitious nature from his father. (AUDIO: The Flying Dutchman)
The people of Sarn descended from a high-technology society into tribalism and superstition. They worshiped Logar, God of the Fire Mountain, and sacrificed unbelievers in fire. (TV: Planet of Fire)
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)
Friday the 13th was considered unlucky according to Rose Tyler. (COMIC: Triskaidekaphobia)
Peter Dickson's mother was superstitious, believing that black cats were unlucky, especially if they had green eyes. Her son didn't share her belief. (PROSE: The Clockwise Man)
Dalek Sec of the Cult of Skaro dismissed ghosts as superstition. (TV: Doomsday)
At the edge of the universe, the Fourteenth Doctor invoked the superstition about salt keeping away Vampires, Ghosts, and Demons and how every grain of salt had to be counted in order to hold back the Not-things. The Doctor later worried to Donna Noble about the consequences of his actions because, while normally doing such a thing wouldn't matter, it could be different at the edge of the universe where the walls were thin, and anything was possible. (TV: Wild Blue Yonder [+]Russell T Davies, Doctor Who 60th Anniversary Specials (BBC One and Disney+, 2023).) Indeed the Doctor's fears were correct because his invoking the superstition and in effect playing a game with the Not-things, allowed the Toymaker to escape from his domain and into N-Space. (TV: The Giggle [+]Russell T Davies, Doctor Who 60th Anniversary Specials (BBC One and Disney+, 2023).)