Splendid beer, on reflection (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' says the letters should be written backwards.
'lager' backwards is 'REGAL'.
(Other definitions for regal that I've seen before include "Kingly or queenly" , "Imperial, majestic" , "Fit for a monarch" , "Royal - lager (anag)" , "'Majestic, royal (5)'" .)