Finally doesn't finish a worldly book (5)
I believe the answer is:
atlas
'a worldly book' is the definition.
'atlas' can be an answer for 'book' (atlas is a kind of book). I'm not certain of the 'a worldly' bit.
'finally doesn't finish' is the wordplay.
'finally' becomes 'at last' (synonyms).
'doesn't finish' means to remove the last letter.
'atlast' with its last letter taken away is 'ATLAS'.
Can you help me to learn more?
(Other definitions for atlas that I've seen before include "Titan who supported the heavens" , "Supporter of the classics" , "Segment of spine" , "I carry a huge weight" , "Size of paper once" .)