Mock one the French Queen rejected (6)
I believe the answer is:
unreal
'mock' is the definition.
(thesaurus)
'one the french queen rejected' is the wordplay.
'one' becomes 'un' (northern English dialect form of 'one').
'the french' becomes 'la' ('the' in French).
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'rejected' says the letters should be written in reverse.
'la'+'er'='laer'
'laer' reversed gives 'real'.
'un'+'real'='UNREAL'
(Other definitions for unreal that I've seen before include "Artificial, insubstantial" , "Not actual or credible" , "Dreamlike" , "Lacking in substance" , "Illusory; amazing" .)