鋭角

1. Origins, structure, and basic meaning

• Structure: Written 鋭角 and read えいかく, it is an angle greater than zero degrees and less than ninety degrees.
• Basic usage: It is drawn with a set square and counted among the angles of a triangle.

2. Common pitfalls and similar expressions

• Boundary with a right angle
  • An angle of exactly ninety degrees is not acute; the opening must be smaller.