Climbing once more, artist falls (7)
I believe the answer is:
niagara
'falls' is the definition.
(thesaurus)
'climbing once more artist' is the wordplay.
'climbing' shows that the letters should be reversed in order (in a down clue, letters climb up).
'once more' becomes 'again' ('again' can be a synonym of 'once more').
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'again' backwards is 'niaga'.
'niaga'+'ra'='NIAGARA'
(Other definitions for niagara that I've seen before include "Large water falls" , "They fall in North America" , "N. American waterfall" , "River linking Lakes Ontario and Erie" , "Great waterfalls on Canadian-US border" .)