Stupid type of angle (6)
I believe the answer is:
obtuse
This clue is a double definition.
'stupid' is the first definition.
(similar in meaning)
'type of angle' is the second definition.
(Other definitions for obtuse that I've seen before include "Orchestra; stripe" , "angle, perhaps" , "(Of angle) between 90deg and 180deg - dull" , "'Dense, slow (6)'" , "Blunt, not sharp or pointed" .)