“Charlie,” to his younger brother, is cocaine (5)
I believe the answer is:
candy
'his younger brother is cocaine' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'charlie to' is the wordplay.
'charlie' becomes 'C' (phonetic alphabet).
'to' becomes 'andy' (I can't justify this - if you can you should give a lot more credence to this answer).
'c'+'andy'='CANDY'
Can you help me to learn more?
(Other definitions for candy that I've seen before include "Sugary sweet" , "Girl's name (diminutive)" , "American confectionary" , "American sweets" , "Crystallised sugar; US sweets" .)