Returned lots I had found dull (6)
I believe the answer is:
stolid
'dull' is the definition.
(similar in meaning)
'returned lots i had' is the wordplay.
'returned' shows that the letters should be reversed in order.
'i had' becomes 'i'd' (I'd).
'lots' reversed gives 'stol'.
'stol'+'id'='STOLID'
'found' acts as a link.
(Other definitions for stolid that I've seen before include "Calm, unanimated" , "Showing little or no interest or emotion" , "Not excitable or emotional" , "'Calm and dependable, showing little emotion (6)'" , "Hard to move" .)