Artist on call spoke (6)
I believe the answer is:
radial
'spoke' is the definition.
(I've seen this before)
'artist on call' is the wordplay.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'on' means one lot of letters go next to another.
'call' becomes 'dial' (I've seen this in another clue).
'ra'+'dial'='RADIAL'
(Other definitions for radial that I've seen before include "Emanating from a central point" , "tire (American)" , "Type of car tyre" , "With lines or spokes from a central point" , "Set out as wheel spokes" .)