Mythical wild East Riding? (4-2)
I believe the answer is:
made-up
'mythical' is the definition.
(thesaurus)
'wild east riding?' is the wordplay.
'wild' becomes 'mad' (similar in meaning).
'east' becomes 'e' (abbreviation).
'riding?' becomes 'up' (I've seen this in other clues).
'mad'+'e'+'up'='MADE-UP'
(Other definitions for made-up that I've seen before include "Fictitious, fabricated" , "Invented, untrue" , "Fictional" , "Put together as in parcel, or put differences aside to become friends again" , "Fictitious, invented" .)