Drink after drug like opium is the best (6,3)
I believe the answer is:
number one
'the best' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'drink after drug like opium' is the wordplay.
I cannot quite understand how this works, but
'drink' could be 'one' (eg 'a cold one') and 'one' is found in the answer.
'drug' could be 'e' (E is another name for ecstasy) and 'e' is found in the answer.
This explanation may well be incorrect...
'is' acts as a link.
Can you help me to learn more?
(Other definitions for number one that I've seen before include "Informally and numerically, oneself" , "arch" , "Yours truly" , "top man?" , "the most important person" .)