Spin jar filled with last of mercury (6)
I believe the answer is:
gyrate
'spin' is the definition.
(synonyms)
'jar filled with last of mercury' is the wordplay.
'jar' becomes 'grate' (make unpleasant sound).
'filled with' is an insertion indicator.
'last of' suggests the final letters.
The final letter of 'mercury' is 'y'.
'grate' going around 'y' is 'GYRATE'.
(Other definitions for gyrate that I've seen before include "Spiral about a point" , "Move spirally" , "Twirl" , "Dance wildly" , "Revolve quickly and repeatedly around one's own axis" .)