Lose cool fighting 1000 (4)

I believe the answer is:

warm

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

'lose cool' is the definition.
I can't tell whether this defines the answer.

'fighting 1000' is the wordplay.
'fighting' becomes 'war'.
'm000' becomes 'm' (roman numeral).
'war'+'m'='WARM'

Can you help me to learn more?

(Other definitions for warm that I've seen before include "Affectionate; heat" , "Slightly hot" , "On the brink of making discovery" , "Getting close to target" , "Passionate; ardent" .)

I've seen this clue in The Irish Independent.

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