A king in brilliant list at back of book? (8)
I believe the answer is:
glossary
'back of book?' is the definition.
'glossary' can be an answer for 'book?' (glossary is a kind of book). I am unsure of the 'back of' bit.
'a king in brilliant list' is the wordplay.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'in' means one lot of letters goes inside another.
'brilliant list' becomes 'glossy' (I can't explain this - if you can you should believe this answer much more).
'a'+'r'='ar'
'ar' going within 'glossy' is 'GLOSSARY'.
'at' is the link.
Can you help me to learn more?
(Other definitions for glossary that I've seen before include "List of explanations of words" , "List of words with meanings" , "Alphabetical list of technical terms" , "List of technical words with definitions" , "where terms are laid out" .)