Begin to consume a large whiskey and stout (8)
I believe the answer is:
stalwart
'stout' is the definition.
(I know that stout can be written as stalwart)
'begin to consume a large whiskey' is the wordplay.
'begin' becomes 'start' (synonyms).
'to consume' indicates putting letters inside.
'large' becomes 'L' (eg in clothes sizes).
'whiskey' becomes 'W' (alpha bravo charlie delta ...).
'a'+'l'+'w'='alw'
'start' enclosing 'alw' is 'STALWART'.
'and' acts as a link.
(Other definitions for stalwart that I've seen before include "Valiant" , "Steadfast" , "Loyalist" , "husky" , "Staunchly faithful" .)