AA kill drunk in compound (6)
I believe the answer is:
alkali
'compound' is the definition.
(alkali is a kind of compound)
'aa kill drunk' is the wordplay.
'drunk' indicates anagramming the letters.
'aa'+'kill'='aakill'
'aakill' with letters rearranged gives 'ALKALI'.
'in' acts as a link.
(Other definitions for alkali that I've seen before include "Soluble compound that turns litmus paper blue" , "Acid-neutralising chemical" , "Non-acid" , "Antacid" , "Compound turning litmus blue" .)