Brook - a security risk? (7)

I believe the answer is:

babbler

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

'brook a security risk?' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

This is the entire clue.

Can you help me to learn more?

I've seen this clue in The Globe and Mail.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.