Line in curse - church becoming pale (6)
I believe the answer is:
blanch
'pale' is the definition.
(synonyms)
'line in curse church' is the wordplay.
'line in curse' becomes 'blan' (I am not sure about this - if you are sure you should believe this answer much more).
'church' becomes 'ch' (common abbreviation).
'blan'+'ch'='BLANCH'
'becoming' acts as a link.
Can you help me to learn more?
(Other definitions for blanch that I've seen before include "woman" , "Go white as with fear" , "Go pale as with fright" , "(Of vegetables) cook briefly in boiling water" , "Make or become pale" .)