Believing in developed cities by day (7)
I believe the answer is:
'believing in' is the definition.
Although both the answer and definition are adjectives, I don't see how they can define each other.
'developed cities by day' is the wordplay.
'developed' indicates anagramming the letters.
'by' says to put letters next to each other.
'day' becomes 'd' (abbreviation for day).
'cities' is an anagram of 'eistic'.
'eistic' after 'd' is 'DEISTIC'.
Can you help me to learn more?
(Other definitions for deistic that I've seen before include "Believing in a supreme being" , "Following one type of religion" .)