Cocky parish priest is seen in posh hotel (6)
I believe the answer is:
uppish
'cocky' is the definition.
(both can mean arrogant)
'parish priest is seen in posh hotel' is the wordplay.
'parish priest' becomes 'pp' (abbreviation for parish priest).
'seen in' indicates putting letters inside.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-u).
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'pp'+'is'='ppis'
'u'+'h'='uh'
'ppis' inserted inside 'uh' is 'UPPISH'.
(Other definitions for uppish that I've seen before include "Pretentious" , "Arrogantly self-assertive" .)