Artist going to bank once in a blue moon (6)
I believe the answer is:
rarely
'once in a blue moon' is the definition.
(I've seen this before)
'artist going to bank' is the wordplay.
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'going to' is a charade indicator (letters next to each other).
'bank' becomes 'rely' (I've seen this before).
'ra'+'rely'='RARELY'
(Other definitions for rarely that I've seen before include "Gas used in fluorescent signs" , "Seldom, not frequently" , "Not very often, seldom in fact" , "once in a blue moon" , "Hardly ever, most infrequently" .)