Iris's bluster -- shameless! (8)
I believe the answer is:
flagrant
'shameless' is the definition.
(thesaurus)
'iris's bluster' is the wordplay.
'iris' becomes 'flag' ('flag' can be a synonym of 'iris').
'bluster' becomes 'rant'.
'flag'+'rant'='FLAGRANT'
(Other definitions for flagrant that I've seen before include "Openly outrageous" , "'Conspicuous, glaring (8)'" , "Of unconcealed outrageousness" , "Very bad and obvious, say offence" , "Shocking" .)