Gas discharge behind VA (6)

I believe the answer is:

vapour

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

'gas discharge behind va' is the definition.
I can't judge whether this definition defines the answer.

'discharge behind va' is the wordplay.
'discharge' becomes 'pour' (I can't explain this - if you can you should believe this answer much more).
'behind' means one lot of letters go next to another.
'pour' after 'va' is 'VAPOUR'.

Can you help me to learn more?

(Other definitions for vapour that I've seen before include "Boast" , "Moisture diffused and suspended in air" , "Liquid in gas form" , "Visible steam or clouds" , "Substance diffused in the air" .)

I've seen this clue in The Independent.

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.