Reference work is finally abridged (5)
I believe the answer is:
atlas
'reference work' is the definition.
(atlas is a kind of reference work)
'finally abridged' is the wordplay.
'finally' becomes 'at last' (synonyms).
'abridged' means to remove the last letter.
'atlast' with its final letter taken away is 'ATLAS'.
'is' is the link.
(Other definitions for atlas that I've seen before include "He had the world on his shoulders" , "African mountain range" , "Titan - map book" , "The first cervical vertebra" , "collection of charts" .)