obtuse

Obtuse is a term used in geometry to describe an angle greater than 90 degrees and less than 180 degrees. It is wider than a right angle but not a straight angle, which measures 180 degrees. A polygon can have an obtuse interior angle; a triangle is obtuse if one of its angles exceeds 90 degrees. Because the sum of the interior angles in a triangle is 180 degrees, an obtuse triangle can have only one obtuse angle, and it can be scalene or isosceles but not equilateral.

In broader mathematical usage, obtuse describes objects that are not sharp. In geometry, the term helps distinguish obtuse angles from acute angles (less than 90 degrees) and right angles (exactly 90 degrees). An obtuse triangle, for example, contains exactly one obtuse angle, with the remaining two angles summing to less than 90 degrees.

Etymology and common usage: the word derives from the Latin obtusus, meaning blunt or dull, and it has been adopted in mathematics to differentiate angles and shapes from acute and right categories. In everyday language, obtuse can also describe dullness in perception or intellect, or a remark that is vague or insensitive.