Toxic intellect admits toxic sides failed (7)
I believe the answer is:
noxious
'toxic' is the definition.
(associated in meaning)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for noxious that I've seen before include "Harmful, toxic" , "Disgusting" , "Harmful, poisonous" , "foul" , "Unwholesome" .)