Trainer possibly gaining weight between fights? (8)

I believe the answer is:

interwar

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'trainer possibly gaining weight between fights?' is the definition.
I can't tell whether this defines the answer.

'trainer possibly gaining weight' is the wordplay.
'possibly' indicates an anagram.
'gaining' means one lot of letters goes inside another.
'weight' becomes 'w' (short for weight).
'trainer' anagrammed gives 'interar'.
'interar' going around 'w' is 'INTERWAR'.

Can you help me to learn more?

(Another definition for interwar that I've seen is " within conflict bounds".)

I've seen this clue in The Telegraph.

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