A party in nude, terribly brazen! (9)
I believe the answer is:
unabashed
'brazen' is the definition.
(I've seen this before)
'a party in nude terribly' is the wordplay.
'party' becomes 'bash' (bash is a kind of party**).
'in' is an insertion indicator.
'terribly' indicates anagramming the letters.
'a'+'bash'='abash'
'nude' anagrammed gives 'uned'.
'abash' placed into 'uned' is 'UNABASHED'.
(Other definitions for unabashed that I've seen before include "confident" , "Brazen" , "Not at all ashamed or embarrassed" , "without embarrassment" , "lacking shame" .)