Celebrity adopting Frenchwoman's speech impediment (7)
I believe the answer is:
stammer
'speech impediment' is the definition.
(stammer is a type of speech impediment)
'celebrity adopting frenchwoman's' is the wordplay.
'celebrity' becomes 'star' (a star is a celebrity or famous person).
'adopting' is an insertion indicator (inserted letters are taken on or adopted).
'frenchwoman' becomes 'mme' (abbreviation for madame).
'star' going around 'mme' is 'STAMMER'.
(Other definitions for stammer that I've seen before include "Speak with difficulty" , "Repeat the beginnings of words" , "Involuntary speech mannerism" , "Speak with common speech impediment" , "delivery problem" .)