Trump, lying American (6)

I believe the answer is:

flatus

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'trump' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

'lying american' is the wordplay.
'lying' becomes 'flat' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'american' becomes 'US' (United States).
'flat'+'us'='FLATUS'

Can you help me to learn more?

(Other definitions for flatus that I've seen before include "wind" , "gas" .)

I've seen this clue in The Independent.

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