Complain about neckwear Charlie's wearing in rehearsal (8)
I believe the answer is:
practice
'rehearsal' is the definition.
(I know that rehearsal can be written as practice)
'complain about neckwear charlie's wearing' is the wordplay.
'complain' becomes 'carp' (carp can informally mean to complain or whinge).
'about' says the letters should be written backwards.
'neckwear' becomes 'tie' (type of neckwear).
'charlie' becomes 'C' (phonetic alphabet: alpha, bravo, charlie etc.).
'wearing' means one lot of letters goes inside another.
'carp' back-to-front is 'prac'.
'tie' going around 'c' is 'tice'.
'prac'+'tice'='PRACTICE'
'in' acts as a link.
(Other definitions for practice that I've seen before include "Habit - procedure" , "Team of doctors" , "It makes perfect, 'tis said" , "'....... what you preach'" , "Use" .)