Changing trains, chap gets bitter (10)
I believe the answer is:
astringent
'bitter' is the definition.
(thesaurus)
'changing trains chap' is the wordplay.
'changing' indicates anagramming the letters.
'chap' becomes 'gent' (I've seen this in other clues**).
'trains' is an anagram of 'astrin'.
'astrin'+'gent'='ASTRINGENT'
'gets' acts as a link.
(Other definitions for astringent that I've seen before include "Lotion" , "Severe - checking the flow of blood" , "acerbic" , "medical preparation" , "biting" .)