Academic taking on significant example of idiocy (6)
I believe the answer is:
donkey
'example of idiocy' is the definition.
'academic taking on significant' is the wordplay.
'academic' becomes 'don' (I've seen this before).
'taking on' means one lot of letters go next to another.
'significant' becomes 'key'.
'don'+'key'='DONKEY'
(Other definitions for donkey that I've seen before include "Braying animal" , "Foolish person; animal" , "Garment associated with building workers" , "Domesticated animal" , "Ass; stupid person" .)