Language is blunt, losing head (4)
I believe the answer is:
erse
'language' is the definition.
(Erse is an example)
'blunt losing head' is the wordplay.
'blunt' becomes 'terse'.
'losing head' means to remove the first letter.
'terse' with its first letter removed is 'ERSE'.
'is' is the link.
(Other definitions for erse that I've seen before include "Old name for Celtic languages" , "Old Gaelic for the seer" , "Old Scots or Irish Gaelic" , "Old language spoken by strange seer" , "Old Celtic language" .)