Overdue book was uplifting (7)
I believe the answer is:
belated
'overdue' is the definition.
(belated means overdue or behind schedule)
'book was uplifting' is the wordplay.
I cannot quite see how this works, but
'book' could be 'b' (abbreviation for book) and 'b' is found within the answer.
The remaining letters 'elated' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for belated that I've seen before include "Coming too late" , "Behind time" , "delayed" , "After the proper time" , "Out of date" .)