Stainer’s notes held by male alto (5)
I believe the answer is:
henna
'stainer's' is the definition.
(I've seen this before)
'notes held by male alto' is the wordplay.
'notes' becomes 'nn' (an abbreviation for note written twice).
'held by' means one lot of letters goes inside another.
'male' becomes 'he' (he refers to a man).
'alto' becomes 'a' (musical abbreviation).
'he'+'a'='hea'
'nn' placed into 'hea' is 'HENNA'.
(Other definitions for henna that I've seen before include "Stainer" , "Shrub used for reddish-brown dye" , "Hair/skin dye" , "Reddish brown dye used on hair" , "Local colour" .)