One artist climbing a palm tree (5)
I believe the answer is:
areca
'a palm tree' is the definition.
(areca is a kind of palm tree)
'one artist climbing' is the wordplay.
'one' becomes 'ace' ('ace' can be a synonym of 'one'**).
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'climbing' says the letters should be written in reverse (in a down clue, letters climb up).
'ace'+'ra'='acera'
'acera' reversed gives 'ARECA'.
(Other definitions for areca that I've seen before include "Sort of nut" , "Tall palm tree" , "Palm with red nuts" , "palm-tree" , "Tropical palm" .)