Habitual drinker (5)
I believe the answer is:
toper
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">habitual drinker</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for toper that I've seen before include "One who drinks to excess" , "Serious drinker" , "Trope for habitual drinker" , "Heavy drinker" , "Someone with a drink problem" .)