Open weary diatribe (8)
I believe the answer is:
flagrant
'open' is the definition.
(thesaurus)
'weary diatribe' is the wordplay.
'weary' becomes 'flag' (both can mean to tire).
'diatribe' becomes 'rant' (I've seen this in other clues).
'flag'+'rant'='FLAGRANT'
(Other definitions for flagrant that I've seen before include "Shocking" , "Patent" , "Barefaced" , "'Conspicuous, glaring (8)'" , "notorious" .)