Exclamation over a book, or antihero in one (4)

I believe the answer is:
ahab
'antihero in one' is the definition.
The definition suggests a singular noun which matches the answer.
'exclamation over a book' is the wordplay.
'exclamation' becomes 'aha' (I have seen 'Exclamation of discovery ' mean 'aha' so perhaps 'exclamation' could also mean 'aha').
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'a book' becomes 'b' (abbreviation for book).
'aha'+'b'='AHAB'
'or' is the link.
Can you help me to learn more?
(Other definitions for ahab that I've seen before include "Captain hunting the whale Moby-Dick" , "Captain in search of Moby Dick" , "Name of captain seeking Moby Dick" , "Jezebel's husband, wicked king in the 'Old testament'" , "sea captain" .)
