I soon gasp fighting this? (6,3)

I believe the answer is:

poison gas

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

'this?' is the definition.
The definition suggests a singular noun which matches the answer.

'i soon gasp fighting' is the wordplay.
'fighting' indicates an anagram (I've seen this in other clues).
'i'+'soon'+'gasp'='isoongasp'
'isoongasp' with letters rearranged gives 'POISON-GAS'.

Can you help me to learn more?

(Other definitions for poison gas that I've seen before include "Eg, sarin or phosgene" , "Such as chlorine" .)

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.