obtuse

of an angle; between 90 and 180 degrees

of a leaf shape; rounded at the apex

lacking in insight or discernment

• “too obtuse to grasp the implications of his behavior”
• “a purblind oligarchy that flatly refused to see that history was condemning it to the dustbin” Jasper Griffin

slow to learn or understand; lacking intellectual acuity

• “so dense he never understands anything I say to him”
• “never met anyone quite so dim”
• “although dull at classical learning, at mathematics he was uncommonly quick” Thackeray
• “dumb officials make some really dumb decisions”
• “he was either normally stupid or being deliberately obtuse”
• “worked with the slow students”