Obtuse

ob·tuse

adjective \äb-ˈtüs, əb-, -ˈtyüs\

: stupid or unintelligent : not able to think clearly or to understand what is obvious or simple

mathematics : not ending in a sharp point : measuring between 90 degrees and 180 degrees

ob·tus·erob·tus·est

Full Definition of OBTUSE

1

a :  not pointed or acute :  blunt

b (1) of an angle :  exceeding 90 degrees but less than 180 degrees (2) :  having an obtuse angle <an obtuse triangle> — see triangle illustration

c of a leaf :  rounded at the free end

2

a :  lacking sharpness or quickness of sensibility or intellect :  insensitive, stupid

b :  difficult to comprehend :  not clear or precise in thought or expression

— ob·tuse·ly adverb

— ob·tuse·ness noun

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How obtuse would one not know what obtuse is and not look up in a dictionary?