Taste had been sampled by mate? (6)
I believe the answer is:
palate
'taste' is the definition.
(palate can mean an ability to distinguish tastes)
'had been sampled by mate?' is the wordplay.
'had been sampled' becomes 'ate'.
'by' is a charade indicator (letters next to each other).
'mate?' becomes 'pal' (both can mean a friend).
'ate' put after 'pal' is 'PALATE'.
(Other definitions for palate that I've seen before include "Liking" , "One may savour" , "A plate (anag.)" , "Roof of the mouth, seat of taste" , "Sense of taste at roof of mouth" .)