Isaac Hayes initially confused about piano mute? (7)
I believe the answer is:
aphasic
'mute?' is the definition.
(thesaurus)
'isaac hayes initially confused about piano' is the wordplay.
'initially' says to take the initial letters.
'confused' indicates an anagram.
'about' means one lot of letters goes inside another.
'piano' becomes 'p' (musical abbreviation).
The initial letter of 'hayes' is 'h'.
'isaac'+'h'='isaach'
'isaach' anagrammed gives 'ahasic'.
'ahasic' enclosing 'p' is 'APHASIC'.
(Other definitions for aphasic that I've seen before include "Unable to use language" , "Speechless because of brain damage; as a chip (anag.)" .)