obtuse

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Lacking quickness of perception or intellect.
• adjective Characterized by a lack of intelligence or sensitivity.
• adjective Not distinctly felt.
• adjective Not sharp, pointed, or acute in form; blunt.
• adjective Having an obtuse angle.
• adjective Botany Having a blunt or rounded tip.

from The Century Dictionary.

• Blunt; not acute or pointed: applied to an angle, it denotes one that is larger than a right angle, or of more than 90°. See cuts under angle.
• In botany, blunt, or rounded at the extremity: as, an obtuse leaf, sepal, or petal.
• Dull; lacking in acuteness of sensibility: stupid: as, he is very obtuse; his perceptions are obtuse.
• Not shrill; obscure; dull: as, an obtuse sound.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Not pointed or acute; blunt; -- applied esp. to angles greater than a right angle, or containing more than ninety degrees.
• adjective Not having acute sensibility or perceptions; not alert, especially to the feelings of others; dull; stupid.
• adjective Dull; deadened.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective zoology Blunt; not sharp.
• adjective Intellectually dull or dim-witted.
• adjective Indirect or circuitous.
• adjective Of sound: deadened or muffled.
• adjective geometry Of an angle: greater than 90 degrees but less than 180 degrees.
• adjective geometry Of a triangle: with one obtuse angle.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective slow to learn or understand; lacking intellectual acuity
• adjective lacking in insight or discernment
• adjective (of a leaf shape) rounded at the apex
• adjective of an angle; between 90 and 180 degrees