Angle between 90 and 180 degrees (6)
I believe the answer is:
obtuse
'angle between 90 and 180 degrees' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for obtuse that I've seen before include "(Of angle) between 90° and 180° - dull" , "Dull or blunt" , "Dim-witted" , "A 3dn between 90 and 180 degrees" , "Slow of understanding" .)