Crossword Genius

Held forth thunderously (7)

Ross

I believe the answer is:

stormed

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'held' is the definition.
The answer and definition can be both to do with contact as well as being past participle verbs.
Perhaps there's an association between them I don't understand?

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Another definition for stormed that I've seen is " Charged".)

I've seen this clue in the Evening Standard.
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