Obvious and excessively large politicians’ promises (10)

I believe the answer is:

manifestos

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'politicians' promises' is the definition.
The answer and definition can be both related to communication as well as being plural nouns.
Perhaps you can see an association between them that I can't see?

'obvious and excessively large' is the wordplay.
'obvious' becomes 'manifest' (similar in meaning).
'and' means one lot of letters go next to another.
'excessively large' becomes 'os' (abbreviation for oversize. I am not sure about the 'excessively' bit.).
'manifest'+'os'='MANIFESTOS'

Can you help me to learn more?

I've seen this clue in The Times.

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