Book with one Greek character or another (4)
I believe the answer is:
beta
'or another' is the definition.
I can't judge whether this definition defines the answer.
'book with one greek character' is the wordplay.
'book' becomes 'b' (abbreviation for book).
'with' means one lot of letters go next to another.
'one greek character' becomes 'eta' (letter from the Greek alphabet).
'b'+'eta'='BETA'
Can you help me to learn more?
(Other definitions for beta that I've seen before include "Second letter of the Greek alphabet" , "Greek letter -- second in order of importance" , "Second-rate" , "Old character" , "software under test" .)