Questionable royal chap arranged to arrest priest (10)
I believe the answer is:
apocryphal
'questionable' is the definition.
('apocryphal' can be similar in meaning to 'questionable')
'royal chap arranged to arrest priest' is the subsidiary indication.
'arranged' indicates an anagram.
'to arrest' indicates putting letters inside.
'priest' becomes 'p' (ecclesiastical abbreviation).
'royal'+'chap'='royalchap'
'royalchap' is an anagram of 'aocryphal'.
'aocryphal' going around 'p' is 'apocryphal'.
(Other definitions for apocryphal that I've seen before include "Fabulous" , "probably made-up" .)