Stop heartless language (6)
I believe the answer is:
finish
'stop' is the definition.
(synonyms)
'heartless language' is the wordplay.
'heartless' means to remove the middle letters.
'language' becomes 'Finnish' (language of Finland).
'finnish' with its centre taken out is 'FINISH'.
(Other definitions for finish that I've seen before include "curtains" , "Patina" , "Polish, perhaps" , "Terminate, conclude" , "train socially" .)