Harpo Marx's little dog (3)

I believe the answer is:

pom

I'm a little stuck... Click here to teach me more about this clue!

'little dog' is the definition.
(Pom is short for Pomeranian)

'harpo marx's' is the wordplay.
'POM' is hidden within the letters.
But, I'm uncertain how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for pom that I've seen before include "English person" , "Australian term for Englishman" , "Australian slang for British migrant" , "Britisher in Oz" , "Disparaging term for English immigrants to the Antipodes" .)

I've seen this clue in the Evening Standard.

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