Definitions of obtuse:

• adjective:   of an angle; between 90 and 180 degrees
• adjective:   of a leaf shape; rounded at the apex
• adjective:   lacking in insight or discernment

  Example: "Too obtuse to grasp the implications of his behavior"

• adjective:   slow to learn or understand; lacking intellectual acuity

  Example: "He was either normally stupid or being deliberately obtuse"