Many a French friend has only an undergarment (8)
I believe the answer is:
camisole
'an undergarment' is the definition.
(camisole is a kind of undergarment)
'many a french friend has only' is the wordplay.
'many' becomes 'c' (C is the Roman numeral for 100).
'a french friend' becomes 'ami' (I've seen this before).
'has' says to put letters next to each other.
'only' becomes 'sole' ('sole' can be a synonym of 'only').
'c'+'ami'+'sole'='CAMISOLE'
(Other definitions for camisole that I've seen before include "Woman's undergarment with shoulder straps" , "Loose underbodice" , "Slip" , "nightwear" , "woman could wear it" .)