Undertone to a most bizarre post at this point (10)

I believe the answer is:

atmosphere

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'undertone' is the definition.
(thesaurus)

'a most bizarre post at this point' is the wordplay.
'bizarre' is an anagram indicator.
'post' becomes 'p' (this might be a standard abbreviation which I don't know about).
'at this point' becomes 'here' (I've seen this before).
'most' is an anagram of 'tmos'.
'a'+'tmos'+'p'+'here'='ATMOSPHERE'

'to' is the link.

Can you help me to learn more?

(Other definitions for atmosphere that I've seen before include "prevailing mood" , "character" , "Feeling" , "Pervading tone or mood" , "Gas surrounding a planet" .)

I've seen this clue in the Irish Times.

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