I had one of the ears of a donkey? (7)
I believe the answer is:
idiotic
'of a donkey?' is the definition.
(donkey can mean a foolish person or idiot)
'i had one of the ears' is the wordplay.
'i had' becomes 'I'd' (I'd).
'one' becomes 'i' (Roman numeral).
'of the ears' becomes 'otic' (otic means relating to the ears).
'id'+'i'+'otic'='IDIOTIC'
(Other definitions for idiotic that I've seen before include "Daft" , "description of Dostoevsky hero?" , "without any point" , "Witless" , "Silly" .)