Crushing tool breaking steeple endlessly (6)
I believe the answer is:
pestle
'crushing tool' is the definition.
(I've seen this before)
'breaking steeple endlessly' is the wordplay.
'breaking' indicates anagramming the letters.
'endlessly' means to remove the last letter.
'steeple' with its last letter taken off is 'steepl'.
'steepl' anagrammed gives 'PESTLE'.
(Other definitions for pestle that I've seen before include "Kitchen item" , "leg of lamb, say" , "Mortar's partner?" , "Tool used in mortar" , "Small club for pounding substances in mortar" .)