1. blunt sound: dùn.

2. not sharp: dull knife|scissors dull. Clumsy; inflexible: sluggish|foolish. (Morphological sound. From jin, from tun, tun is also sound. "Tun" means "curl", "wrap". The combination of "jin" and "tun" means "metal blade curling". (Original meaning: metal blade curling)

3, obtuse angle is greater than the right angle is smaller than the flat angle of the angle. If a is an obtuse angle, then 90°

4. An obtuse triangle is called an obtuse triangle if one of its interior angles is obtuse.