Language of ranter sermonising (4)
I believe the answer is:
erse
'language' is the definition.
(Erse is an example)
'of ranter sermonising' is the wordplay.
'of' says the answer is hidden in the clue.
'ERSE' is hidden in the letters of 'ranter sermonising'.
(Other definitions for erse that I've seen before include "Celtic tongue" , "Old language spoken by strange seer" , "Irish Gaelic language" , "Possibly the language" , "Old name for Celtic languages" .)