Caustic (4)
'caustic' is the definition.
(synonyms)
This is all the clue.
(Other definitions for acid that I've seen before include "It is neutralised by alkali" , "Tart - keen - sort of house party" , "Substance with pH of less than 7" , "Drug, tart" , "Morose" .)
'caustic' is the definition.
(I know that caustic can be written as mordant)
This is all the clue.
(Other definitions for mordant that I've seen before include "Corrosive" , "(Of wit) sharp, critical" , "Caustic" , "Waspish" , "Acrimonious" .)
'caustic' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for harsh that I've seen before include "Severe - unkind" , "'Severe, rough (5)'" , "Severe and disagreeable" , "Raucous - austere - bitter" , "Draconian" .)