Dao swords were Chinese swords with curved blades.
In 1807m the Thirteenth Doctor, Yasmin Khan, Dan Lewis, Zheng Yi Sao and Sin Ji-Hun used dao swords to fight the Sea Devils led by Marsissus. (TV: Legend of the Sea Devils)
Chinese magician Li H'sen Chang used a dao sword to threaten Mr Sin in his act at the Regency Theatre. (TV: The Talons of Weng-Chiang)