Curious how day’s dim (7)
I believe the answer is:
shadowy
'dim' is the definition.
(I know that dim can be written as shadowy)
'curious how day's' is the wordplay.
'curious' indicates anagramming the letters.
'how'+'days'='howdays'
'howdays' with letters rearranged gives 'SHADOWY'.
(Other definitions for shadowy that I've seen before include "Why soda? (anag)" , "hazy" , "Obscure, dark" , "Insubstantial" , "Obscure; dim" .)