50 with a king by unearthly American feature (4,4)
I believe the answer is:
lake erie
'american feature' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'50 with a king by unearthly' is the wordplay.
'50' becomes 'l' (Roman numeral).
'with' says to put letters next to each other.
'a king by' becomes 'ak' (I can't explain this - if you can you should believe this answer much more).
'unearthly' becomes 'eerie' (I've seen this before).
'l'+'ak'+'eerie'='LAKE ERIE'
Can you help me to learn more?
(Other definitions for lake erie that I've seen before include "lots of water" , "One of the five Great ones in North America" .)