Brunel meets Virginia in pub, but fruitlessly (2,4)
I believe the answer is:
in vain
'fruitlessly' is the definition.
(I've seen this in another clue)
'brunel meets virginia in pub' is the wordplay.
'brunel' becomes 'I' (where the crossword setter is 'Brunel').
'meets' is a charade indicator (letters next to each other).
'virginia' becomes 'va' (US state abbreviation).
'in' means one lot of letters goes inside another.
'pub' becomes 'inn' (an inn is a type of pub).
'i' put after 'va' is 'vai'.
'vai' inserted into 'inn' is 'IN VAIN'.
'but' is the link.
(Other definitions for in vain that I've seen before include "Without achieving anything" , "useless" , "Fruitlessly" , "Uselessly, to no avail" , "Uselessly, without result" .)