Swear in empty town pub (6)
I believe the answer is:
tavern
'pub' is the definition.
(a tavern is a pub or inn)
'swear in empty town' is the wordplay.
'swear' becomes 'aver' (synonyms).
'in' means one lot of letters goes inside another.
'empty' suggests removing the centre.
'town' with its centre removed is 'tn'.
'aver' inserted within 'tn' is 'TAVERN'.
(Other definitions for tavern that I've seen before include "An old inn or public house" , "Local" , "where drink is available" , "Old song: 'There is a ...... in the town, in the town'" , "An old inn or hostelry" .)