A monarch may meet oriental in secret (6)
I believe the answer is:
arcane
'secret' is the definition.
(thesaurus)
'a monarch may meet oriental' is the wordplay.
'monarch' becomes 'r' (r is abbreviation for rex).
'may' becomes 'can' ('can' can be a synonym of 'may'**).
'meet' means one lot of letters go next to another.
'oriental' becomes 'e'.
'a'+'r'+'can'+'e'='ARCANE'
'in' acts as a link.
(Other definitions for arcane that I've seen before include "Mysteriouss or secret" , "deep" , "Requiring secret or mysterious knowledge" , "Mysterious like a crane" , "Abstruse, mysterious" .)