Spear dropping on Marx (5)

I believe the answer is:

harpo

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'marx' is the definition.
(Harpo Marx)

'spear dropping on' is the wordplay.
'spear' becomes 'harp' (I can't explain this - if you can you should give a lot more credence to this answer).
'dropping' suggests taking the first letters (I've seen 'drop of' mean this).
The first letter of 'on' is 'o'.
'harp'+'o'='HARPO'

Can you help me to learn more?

(Other definitions for harpo that I've seen before include "One of the Marx Brothers" , "brother who never speaks" , "silent film star" , "Silent Marx brother" , "The mute Marx Brother" .)

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