Alcoholic is not missing heads (3)
I believe the answer is:
sot
'alcoholic' is the definition.
(thesaurus)
'not missing heads' is the wordplay.
I cannot really see how this works, but
'not' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
The remaining letters 'st' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'is' acts as a link.
Can you help me to learn more?
(Other definitions for sot that I've seen before include "Lush" , "Boozer" , "A chronic drinker" , "One drinks" , "Habitual drunkard" .)