Whisky kept in jar? Yes (3)
I believe the answer is:
rye
'whisky' is the definition.
(rye whisky is a kind of whisky)
'kept in jar? yes' is the wordplay.
'kept in' indicates a hidden word.
'RYE' can be found hidden inside 'jar yes'.
(Other definitions for rye that I've seen before include "Burns's body came through" , "East Sussex resort" , "Whiskey ingredient" , "Grain crop" , "Cereal grain" .)