Stupid, resembling one that's ''one over the eight'' (7)
I believe the answer is:
'stupid' is the definition.
(I've seen this before)
'one that's 'one over the eight'' is the wordplay.
'one that' becomes 'asi' (I can't explain this - if you can you should give a lot more credence to this answer).
''one over the eight'' becomes 'nine' (nine is one more than eight).
'resembling' acts as a link.
(Other definitions for asinine that I've seen before include "Daft" , "Jenny's often like this" , "Foolish like donkey" , "simple" , "Is Annie? (Anag)" .)