A very piercing acidic taste (6)
I believe the answer is:
savour
'taste' is the definition.
(savouring is a kind of tasting)
'a very piercing acidic' is the wordplay.
'a very' becomes 'av' (I've seen this in other clues).
'piercing' means one lot of letters goes inside another (some letters pierce a hole in others).
'acidic' becomes 'sour' ('sour' can be similar in meaning to 'acidic').
'av' inserted inside 'sour' is 'SAVOUR'.
(Other definitions for savour that I've seen before include "Taste to the full" , "Enjoy the flavour" , "Relish, enjoy" , "Taste, relish" , "Thoroughly enjoy" .)