Vapour right out of a brook (5)

I believe the answer is:

steam

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

'vapour' is the definition.
(I know that steam is a type of vapour)

'right out of a brook' is the wordplay.
I cannot quite understand how this works, but
'a' is present in the answer.
The remaining letters 'stem' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for steam that I've seen before include "Form of water" , "Energy (colloq.)" , "Speed" , "Vapour; energy" , "Kettle emission" .)

I've seen this clue in The Irish News.

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