We don't have synonyms for horn angle yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are hour angle.
(n) :
A curvilinear 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.
(n) :
A curvilinear 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.