Oven, hot once more (5)
I believe the answer is:
again
'once more' is the definition.
(synonyms)
'oven hot' is the wordplay.
'oven' becomes 'aga' (type of large oven).
'hot' becomes 'in' (both can mean fashionable).
'aga'+'in'='AGAIN'
(Other definitions for again that I've seen before include "Repeatedly" , "10 10 [AGAIN" , "Here we go ___" , "On the other hand" , "return" .)