There's not much on Sunday or Monday (4)
I believe the answer is:
whit
'monday' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for whit that I've seen before include "Very small part - Christian festival" , "Iota" , "Tiny amount; a church Sunday" , "Pentecost (abbrev.)" , "Festival week" .)