Abstainer (11)
I believe the answer is:
teetotaller
'abstainer' is the definition.
(I know that teetotaller is a type of abstainer)
This is the entire clue.
(Other definitions for teetotaller that I've seen before include "no supper!" , "Non-drinker" , "Rechabite" , "as observant Muslim, say" , "One dry" .)