Mortar's mate (6)
I believe the answer is:
pestle
'mortar's mate' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pestle that I've seen before include "Small club for use with mortar" , "Small club, goes with mortar" , "Kitchen item" , "It grinds in a mortar" , "found at pound shop?" .)