Caustic substance (4)
'caustic substance' 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 "Caustic and biting" , "Bitter substance" , "- - -drop, sweet" , "Battery fluid" , "Drug, tart" .)
(Other definitions for lime that I've seen before include "white caustic earth" , "White substance used in cement" , "alkaline" , "Sharp-tasting fruit" , "Bright light green" .)
'caustic substance' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lye that I've seen before include "solution that comes out in the wash?" , "Strong alkaline solution" , "Alkali washing solution" , "caustic liquid" , "Strongly alkaline wash" .)