World book finally abridged (5)
I believe the answer is:
'world book' is the definition.
(I've seen this before)
'finally abridged' is the wordplay.
'finally' becomes 'atlast' ('at last' can be a synonym of 'finally').
'abridged' means to remove the last letter.
'atlast' with its final letter removed is 'ATLAS'.
(Other definitions for atlas that I've seen before include "travel book" , "One greatly burdened" , "Mythological Titan (involved with the world of maps?)" , "Cartographer's work" , "God" .)