What's left on the day is fair (8)
I believe the answer is:
balanced
'is fair' is the definition.
(I've seen this in another clue)
'what's left on the day' is the wordplay.
I cannot quite see how this works, but
'left' could be 'al' (I've seen this in other clues) and 'al' is located in the answer.
'day' could be 'd' (abbreviation for day) and 'd' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for balanced that I've seen before include "With both sides equal" , "In a state of equilibrium" , "Having weight equally distributed" , "Composed - unbiased" , "Steady - objective" .)