A horn angle, also called a cornicular angle, is a type of curvilinear angle defined as the angle formed between a circle and a straight line tangent to it, or, more generally, the angle formed between two curves at a point where they are tangent to each other. It is of interest in the history of geometry because since its unusual properties were discussed by mathematicians from the 13th to the 17th centuries.

External links

• David E. Joyce, "Definition 8" Euclid's Elements Book I