For example, grass cultivated to intrude (7)

I believe the answer is:

aggress

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

'intrude' is the definition.
Although both the answer and definition are verbs in their base form, I cannot understand how one could define the other.

I don't understand the rest of the clue.

Can you help me to learn more?

(Another definition for aggress that I've seen is " begin a quarrel".)

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

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