White loaf to stop a short period of fasting (7)
I believe the answer is:
albumen
'white' is the definition.
(white of an egg)
'loaf to stop a short period of fasting' is the wordplay.
'loaf' becomes 'bum' (both can mean to laze around).
'to stop' is an insertion indicator.
'short' means to remove the last letter.
'period of fasting' becomes 'Lent' (fast leading up to Easter).
'lent' with its last letter taken away is 'len'.
'a'+'len'='alen'
'bum' going within 'alen' is 'ALBUMEN'.
(Other definitions for albumen that I've seen before include "Egg's white" , "Egg-white" , "White poacher" , "The white part of an egg" .)