Wonderful fireplace, by the sound of it (5)
I believe the answer is:
great
'wonderful' is the definition.
(I know that wonderful can be written as great)
'fireplace by the sound of it' is the wordplay.
'fireplace' becomes 'grate' (grate can mean a fireplace).
'by the sound of it' indicates a 'sounds like' (homophone) clue.
'grate' sounds like 'GREAT'.
(Other definitions for great that I've seen before include "Of major significance - very good" , "Peter the -, Russ. tsar" , "Grand" , "Considerably above average" , "Wonderful" .)