Only book on Channel area (6)
I believe the answer is:
solent
'channel area' is the definition.
The definition suggests a singular noun which matches the answer.
'only book on' is the wordplay.
'only' becomes 'sole' (synonyms).
'book' becomes 'NT' (New Testament).
'on' says to put letters next to each other.
'sole'+'nt'='SOLENT'
Can you help me to learn more?
(Other definitions for solent that I've seen before include "Strait north of Isle of Wight" , "Confine as a prisoner" , "South coast channel" , "Lets on to be an English waterway" , "Channel N. of IOW" .)