Potentially painful precipitation (4)
I believe the answer is:
hail
'potentially painful precipitation' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for hail that I've seen before include "Greet, call or salute" , "An ancient Roman hello" , "Precipitation - old greeting" , "Old Roman salute, or frozen pellets" , "wintry weather" .)