Astringent (7)
'astringent' is the definition.
(I know that astringent can be written as styptic)
This is all the clue.
(Other definitions for styptic that I've seen before include "Checking blood flow like shaving pencil" , "Stopping bleeding" , "This pencil checks bleeding as from shaving" .)
(Other definitions for caustic that I've seen before include "Chemically burning" , "Acrimonious - sarcastic" , "Burning, corroding" , "Acrid" , "Bitter - corrosive" .)