Knight absorbed by one friar further on in the book ... (5)
I believe the answer is:
infra
'in the book' is the definition.
I can't tell whether this defines the answer.
'knight absorbed by one friar further on' is the wordplay.
'knight' becomes 'n' (chess abbreviation).
'absorbed by' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'friar' becomes 'fr' (abbreviation).
'further on' becomes 'a' (I can't justify this - if you can you should believe this answer much more).
'i'+'fr'='ifr'
'n' put within 'ifr' is 'infr'.
'infr'+'a'='INFRA'
Can you help me to learn more?
(Other definitions for infra that I've seen before include "Dig is demeaning" , "Beneath (esp. 15)" , "Latin adverb meaning below or further on in book" , "Below (as prefix)" , "-- Dig means degrading" .)