Curse builder about front of loo back of Boggabri (7)
I believe the answer is:
malison
'curse' is the definition.
(archaic term for a curse)
'builder about front of loo back of boggabri' is the wordplay.
'builder' becomes 'mason' (I've seen this before).
'about' means one lot of letters goes inside another.
'front of' says to take the initial letters.
'back of' suggests the final letters.
The initial letter of 'loo' is 'l'.
The last letter of 'boggabri' is 'i'.
'l'+'i'='li'
'mason' enclosing 'li' is 'MALISON'.
(Another definition for malison that I've seen is " Once curse".)