Composer hid the French chemical (6)
I believe the answer is:
bleach
'chemical' is the definition.
(I've seen this before)
'composer hid the french' is the wordplay.
I cannot quite understand how this works, but
'the french' could be 'le' and 'le' is found in the answer.
'composer' could be 'bach' (Bach is an example) and 'bach' is located in the leftover letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for bleach that I've seen before include "Get lighter" , "Go white" , "Disinfect" , "Agent that makes things white or colourless" , "Lighten" .)