Pioneer, endlessly tough drinker in bouts? (9)
I believe the answer is:
harbinger
'pioneer' is the definition.
(thesaurus)
'endlessly tough drinker in bouts?' is the wordplay.
'endlessly' means to remove the last letter.
'tough' becomes 'hard' (synonyms).
'drinker in bouts?' becomes 'binger' (I am not sure about this - if you are sure you should believe this answer much more).
'hard' with its final letter removed is 'har'.
'har'+'binger'='HARBINGER'
Can you help me to learn more?
(Other definitions for harbinger that I've seen before include "One announcing approach" , "It signals the future" , "Early sign" , "omen" , "It indicates the future" .)