Bad egg is one decomposing (6)

I believe the answer is:

rotter

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'is one decomposing' is the definition.
(I've seen this before)

'bad egg' is the wordplay.
'bad' becomes 'rot' (I've seen this before).
'egg' becomes 'ter' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'rot'+'ter'='ROTTER'

Can you help me to learn more?

(Other definitions for rotter that I've seen before include "one going bad?" , "One not to be honoured" , "Despicable person" , "One decomposing" , "Scoundrel" .)

I've seen this clue in The Sun.

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