Finally abridged book of maps (5)
I believe the answer is:
atlas
'book of maps' is the definition.
('atlas' can be a synonym of 'book of maps')
'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 "I carry a huge weight" , "One greatly burdened" , "It appears at the top of the spine" , "Chart book" , "The first cervical vertebra" .)