I entered dream home - in Spain suitably enough (7)
I believe the answer is:
'i' is the definition.
Both the definition and answer are singular nouns.
Maybe there's a link between them I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for castile that I've seen before include "Elastic (anag) -- region of Spain" , "Old Spanish kingdom" , "Elastic region in central Spain" , "former Spanish kingdom" .)