Cheeky underwear getting Frenchman's nose up (6)
I believe the answer is:
brazen
'cheeky' is the definition.
(thesaurus)
'underwear getting frenchman's nose up' is the wordplay.
'underwear' becomes 'bra' (bra is a type of undergarment).
'getting' means one lot of letters go next to another.
'frenchman's nose' becomes 'nez' ('nose' in French).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'nez' back-to-front is 'zen'.
'bra'+'zen'='BRAZEN'
(Other definitions for brazen that I've seen before include "Unashamedly flagrant" , "Shameless and bold - resembling brass" , "Bold-faced" , "Forward" , "Impudent, shameless" .)