Screen I wrenched open (7)
I believe the answer is:
sincere
'open' is the definition.
(I've seen this in another clue)
'screen i wrenched' is the wordplay.
'wrenched' indicates anagramming the letters.
'screen'+'i'='screeni'
'screeni' is an anagram of 'SINCERE'.
(Other definitions for sincere that I've seen before include "straightforward" , "Open and genuine, not deceitful" , "'Genuine, not deceitful (7)'" , "Unaffected" , "Unfeigned, genuine" .)