Marx, at a single reading initially, who aimed to finish Moby Dick (9)
I believe the answer is:
harpooner
'marx at a single reading initially who aimed to finish moby dick' is the definition.
The definition suggests a singular noun which matches the answer.
'marx at a single reading initially' is the wordplay.
'marx' becomes 'harpo' (Harpo Marx).
'at' means one lot of letters go next to another.
'a single' becomes 'one' (a single thing - only one).
'initially' suggests taking the first letters.
The initial letter of 'reading' is 'r'.
'harpo'+'one'+'r'='HARPOONER'
Can you help me to learn more?
(Other definitions for harpooner that I've seen before include "I do for whales" , "killer at sea" .)