Burning a bra, to start with, then loaf (6)
I believe the answer is:
ablaze
'burning' is the definition.
(I've seen this in another clue)
'a bra to start with then loaf' is the wordplay.
'to start with' says to take the initial letters.
'then' says to put letters next to each other.
'loaf' becomes 'laze' (as in to loaf or laze around idly).
The initial letter of 'bra' is 'b'.
'a'+'b'+'laze'='ABLAZE'
(Other definitions for ablaze that I've seen before include "Having been fired" , "Flaming; on fire" , "Bright" , "On fire, burning" , "Fiery" .)