Arnold could confuse him with Roland (6)
I believe the answer is:
ronald
'arnold could confuse him with roland' is the definition.
The definition suggests a singular noun which matches the answer.
'him with roland' is the wordplay.
'him' becomes 'ron' (short for Ronald).
'with' says to put letters next to each other.
'roland' becomes 'ald' (I can't explain this - if you can you should believe this answer much more).
'ron'+'ald'='RONALD'
Can you help me to learn more?
(Other definitions for ronald that I've seen before include "The late President Reagan" , "Mr Reagan" , "Chap" , ". . . . . . Reagan, former US president" .)