Extraordinary numeral changed after subtraction of thousand (6)
I believe the answer is:
unreal
'extraordinary' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
(Other definitions for unreal that I've seen before include "Not actually existing" , "Lacking material form" , "fake" , "Illusory, imaginary" , "Fanciful" .)