Plummeted; hill (4)
I believe the answer is:
fell
This clue is a double definition.
'plummeted' is the first definition.
(I've seen this in another clue)
'hill' is the second definition.
(I've seen this before)
(Other definitions for fell that I've seen before include "High moorland or unforested hill in the UK" , "lambs > went down > hill" , "animal skin" , "Chop down" , "Mountain - lost footing - deadly" .)