Beer, on reflection, is splendid (5)
I believe the answer is:
regal
'splendid' is the definition.
(I've seen this in another clue)
'beer on reflection' is the wordplay.
'beer' becomes 'lager' (type of beer).
'on reflection' shows that the letters should be reversed in order.
'lager' reversed gives 'REGAL'.
'is' is the link.
(Other definitions for regal that I've seen before include "Fit for a king" , "Portable organ" , "Befitting a monarch" , "Fit for a monarch" , "Royal - 5 down (anag)" .)