Partly persuade the realists to become spiritual (8)
I believe the answer is:
ethereal
'spiritual' is the definition.
(I've seen this before)
'partly persuade the realists to' is the wordplay.
'partly' indicates the answer is hidden within the clue.
'ETHEREAL' is hidden in the letters of 'persuade the realists to'.
'become' acts as a link.
(Other definitions for ethereal that I've seen before include "gossamer" , "Like fairies" , "Extremely delicate and light, not of this world" , "Impalpable" , "Insubstantial or heavenly" .)