On reflection, met for a drink (5)
I believe the answer is:
decaf
'for a drink' is the definition.
(decaffeinated coffee)
'on reflection met' is the wordplay.
'on reflection' is a reversal indicator.
'met' becomes 'faced' (facing is a kind of meeting).
'faced' backwards is 'DECAF'.
(Other definitions for decaf that I've seen before include "Type of coffee" , "Non-alcoholic drink" , "Cup substitute missing kick" , "Less stimulating coffee?" , "Style of coffee" .)