The Mexican beverage made from corn flour, water, and often cinnamon is atole.
Atole is a traditional hot, thick masa-based drink with roots in Mesoamerica. In Mexico, it is commonly prepared with masa or corn hominy flour, water, and sweeteners such as piloncillo. Cinnamon, vanilla, guava, or other fruit may be added for flavor. The mixture is heated until it develops a smooth, lightly porridge-like consistency.
The drink is closely associated with tamales, which are often served alongside it for breakfast, at festivals, or during cold-weather gatherings. Atole is especially prominent during Día de los Muertos on November 2 and during Las Posadas, the Christmas-season celebrations.
Champurrado is best understood as a chocolate-flavored type of atole, not a completely unrelated beverage. Tejate is another traditional corn-based Mexican drink, but it is generally served cold and includes ingredients such as cacao and the flowers of the rosita de cacao. Horchata is usually a sweet rice- or grain-based drink, often served chilled. Those differences make atole the canonical answer to this description.