Regular's confident in alcoholic drink (8)
I believe the answer is:
measured
'regular's' is the definition.
(thesaurus)
'confident in alcoholic drink' is the wordplay.
'confident' becomes 'sure' ('sure' can be similar in meaning to 'confident').
'in' indicates putting letters inside.
'alcoholic drink' becomes 'mead' (I've seen this before).
'sure' put within 'mead' is 'MEASURED'.
(Other definitions for measured that I've seen before include "Made sure (anag.)" , "Determine dimensions" , "Dare Muse be regular in movement" , "Sized; carefully chosen" , "Unhurried and with care and dignity" .)