Book a very good act (4,5)
I believe the answer is:
beau geste
'act' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe you can see a link between them that I don't see?
'book a very good' is the wordplay.
I cannot really understand how this works, but
'book' could be 'b' (abbreviation for book) and 'b' is found in the answer.
'a' is within the answer.
'good' could be 'g' (abbreviation) and 'g' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for beau geste that I've seen before include "magnanimous act" , "Wren's work" , "Gracious act (Fr.); film" , "Noble act; French foreign legion novel" .)