Half seen prior to bar meeting (9)
I believe the answer is:
encounter
'meeting' is the definition.
('encounter' can be a synonym of 'meeting')
'half seen prior to bar' is the wordplay.
'half' means to take half the letters.
'prior to' says to put letters next to each other.
'bar' becomes 'counter' (I've seen this before**).
'seen' halved is 'en'.
'en'+'counter'='ENCOUNTER'
(Other definitions for encounter that I've seen before include "Meet; confrontation" , "Unexpected meeting" , "tackle" , "Come upon, meet" , "battle" .)