Geography book finally abridged (5)
I believe the answer is:
atlas
'geography book' is the definition.
(I've seen this in another clue)
'finally abridged' is the wordplay.
'finally' becomes 'at last' (synonyms).
'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 "A geog. book; N. African range" , "Titan who held up the sky" , "Titan who bore the sky on his shoulders" , "The first cervical vertebra" , "One of the Titans" .)