Time to avoid pithy language (4)
I believe the answer is:
erse
'language' is the definition.
(historical term for Scottish Gaelic)
'time to avoid pithy' is the wordplay.
'time' becomes 't' (abbreviation).
'to avoid' is a deletion indicator.
'pithy' becomes 'terse' (I've seen this before).
'terse' with 't' taken out is 'ERSE'.
(Other definitions for erse that I've seen before include "Old Scots or Irish Gaelic" , "Old Gaelic for the seer" , "Possibly the language" , "Name sometimes given to languages of the Celts in Ireland and Scotland" , "Old language spoken by strange seer" .)