Melted cheese on hot toast (7)
I believe the answer is:
rarebit
'melted cheese on hot toast' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for rarebit that I've seen before include "which the Welsh take down?" , "Cheesy snack" , "Cheese/toast savoury" , "Cheese on toast - arbiter (anag)" , "Cooked cheese on toast" .)