Imagine Aesop pushing retrograde content (7)
I believe the answer is:
suppose
'imagine' is the definition.
(I know that imagine can be written as suppose)
'aesop pushing retrograde content' is the wordplay.
'content' indicates a hidden word (letters contained within the clue).
'retrograde' says the letters should be written backwards.
'esoppus' is hidden in the letters of 'aesop pushing'.
'esoppus' backwards is 'SUPPOSE'.
(Other definitions for suppose that I've seen before include "Assume, imagine" , "Judge" , "Put forward - imagine" , "Expect" , "Picture" .)