Crack from cleric, idiot in church (8)
I believe the answer is:
crevasse
'crack' is the definition.
(I know that crevasse is a type of crack)
'cleric idiot in church' is the wordplay.
'cleric' becomes 'rev' (abbreviation for Reverend).
'idiot' becomes 'ass' (I've seen this in another clue).
'in' is an insertion indicator.
'church' becomes 'CE' (abbreviation for Church of England).
'rev'+'ass'='revass'
'revass' placed into 'ce' is 'CREVASSE'.
'from' acts as a link.
(Other definitions for crevasse that I've seen before include "big split" , "Deep glacial fissure" , "Sever sac (anag)" , "Deep glacial crack" , "13 in a glacier" .)