Confine to a half of bitter in the pub (6)
I believe the answer is:
intern
'confine' is the definition.
(thesaurus)
'a half of bitter in the pub' is the wordplay.
'a half of' means to take half the letters.
'in the' is an insertion indicator.
'pub' becomes 'inn' (I've seen this before).
'bitter' cut in half is 'ter'.
'ter' placed into 'inn' is 'INTERN'.
'to' is the link.
(Other definitions for intern that I've seen before include "Hospital worker" , "Confine to camp" , "Shut up" , "Imprison (eg, alien) as a precautionary measure" , "to keep under lock and key" .)