Once more, rising artist falls (7)
I believe the answer is:
niagara
'falls' is the definition.
(thesaurus)
'once more rising artist' is the wordplay.
'once more' becomes 'again' ('again' can be a synonym of 'once more').
'rising' says the letters should be written in reverse (going up in a down clue).
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'again' written backwards gives 'niaga'.
'niaga'+'ra'='NIAGARA'
(Other definitions for niagara that I've seen before include "Great waterfalls on US-Canada border" , "& 22 Down North American cascade" , "Famous Falls once walked by Blondin" , "A lot of falling water" , "N American river and Falls" .)