Chairman Mao at last playing instrument (9)
I believe the answer is:
harmonica
'instrument' is the definition.
(I know that harmonica is a type of free-reed instrument)
'chairman mao at last playing' is the wordplay.
'at last' says to take the final letters.
'playing' indicates an anagram.
The last letter of 'mao' is 'o'.
'chairman'+'o'='chairmano'
'chairmano' anagrammed gives 'HARMONICA'.
(Other definitions for harmonica that I've seen before include "It's blown" , "Blow me!" , "Small wind instrument" , "An alternative mouth-organ" , "musical instrument" .)