Piano and stringed instrument returned by worker complaining (8)
I believe the answer is:
petulant
'complaining' is the definition.
(thesaurus)
'piano and stringed instrument returned by worker' is the wordplay.
'piano' becomes 'p'.
'and' says to put letters next to each other.
'stringed instrument' becomes 'lute' (lute is a kind of stringed instrument).
'returned' is a reversal indicator.
'by worker' becomes 'ant' (worker is a type of ant. I am not sure about the 'by' bit.).
'lute' backwards is 'etul'.
'p'+'etul'+'ant'='PETULANT'
(Other definitions for petulant that I've seen before include "Peevish, surly" , "Easily irritated" , "Pouting" , "Peevish, irritable" , "Fractious, pouty" .)