Artist returning aid — National Trust happy? (7)
I believe the answer is:
radiant
'happy?' is the definition.
(thesaurus)
'artist returning aid national trust' is the wordplay.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'returning' says the letters should be written in reverse.
'national trust' becomes 'nt'.
'aid' back-to-front is 'dia'.
'ra'+'dia'+'nt'='RADIANT'
(Other definitions for radiant that I've seen before include "looking happy" , "Sending out light, glowing" , "Shining - happy" , "Effulgent" , "Splendid; heater type" .)