Finally book for the end of August (2,4)
I believe the answer is:
at last
'finally' is the definition.
(synonyms)
'book for the end of august' is the wordplay.
'book' becomes 'atlas' (atlas is a kind of book).
'for' says to put letters next to each other.
'the end of' suggests the final letters.
The last letter of 'august' is 't'.
'atlas'+'t'='AT LAST'
(Other definitions for at last that I've seen before include "Finally, having waited a long time" , "Finally, after a long wait" , "Finally, after much delay" , "'In the end (2,4)'" , "Where a snob worked" .)