noun
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geometryan angle that measures less than 90 degrees.
An acute angle is an angle that measures less than 90 degrees.
An angle is the figure formed by two rays sharing a common endpoint called the vertex. Its size, measured in degrees or radians, is the amount of rotation needed to align one ray with the other.
A right angle is an angle of exactly 90 degrees, a quarter of a full turn.
A perpendicular angle is equal to a quarter of a full rotation. A perpendicular angle is measured as 90 degrees or π/2 radians.
An obtuse angle is an angle that measures more than 90 degrees but less than 180 degrees. It is larger than a right angle and smaller than a straight angle.