Corrosive compound (4)
I believe the answer is:
acid
'corrosive compound' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for acid that I've seen before include "Tart, sour" , "Sarcastic (could be sulphuric?)" , "It is neutralized by alkali" , "Polluted precipitation" , "- - -drop, sweet" .)