Regularly repressed language (4)
I believe the answer is:
erse
'language' is the definition.
(Erse is an example)
'regularly repressed' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'repressed' are 'ERSE'.
(Other definitions for erse that I've seen before include "Celtic tongue" , "Possibly the language" , "Old Celtic language" , "Name sometimes given to languages of the Celts in Ireland and Scotland" , "Old Scots or Irish Gaelic" .)