Message - a wire carrying some weight (9)

I believe the answer is:

cablegram

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

'message' is the definition.
(I know that cablegram is a type of telegram)

'a wire carrying some weight' is the wordplay.
'a wire' becomes 'cable' (cable is a kind of wire).
'carrying some weight' becomes 'gram' (I can't explain this - if you can you should believe this answer much more).
'cable'+'gram'='CABLEGRAM'

Can you help me to learn more?

(Another definition for cablegram that I've seen is " Urgent message".)

I've seen this clue in the Sydney Morning Herald.

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