Hilarious colossus depicting Neptune (3,5)

I believe the answer is:

gas giant

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'neptune' is the definition.
I know nothing about this answer so I can't tell whether this works.

'hilarious colossus' is the wordplay.
'hilarious' becomes 'gas' (I am not sure about this - if you are sure you should believe this answer much more).
'colossus' becomes 'giant' (synonyms).
'gas'+'giant'='GAS GIANT'

'depicting' acts as a link.

Can you help me to learn more?

I've seen this clue in The Irish Times.

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