Almost damage girl's musical instrument (9)
I believe the answer is:
harmonica
'musical instrument' is the definition.
(I know that harmonica is a type of musical instrument)
'almost damage girl's' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'damage' becomes 'harm' (synonyms).
'girl' becomes 'monica' (girl's name).
'harm' with its final letter taken away is 'har'.
'har'+'monica'='HARMONICA'
(Other definitions for harmonica that I've seen before include "Larry Adler's instrument" , "glasses of water" , "Small wind instrument" , "musical instrument" , "Blow me!" .)