Compounds ten days with a fateful one (7)

I believe the answer is:

iodides

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'compounds' is the definition.
(iodide is a kind of compound)

'ten days with a fateful one' is the wordplay.
'ten' becomes 'IO' (IO resembles i0).
'days' becomes 'd' (abbreviation for days).
'with' means one lot of letters go next to another.
'a fateful one' becomes 'ides' (I can't explain this - if you can you should believe this answer much more).
'io'+'d'+'ides'='IODIDES'

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I've seen this clue in The Times.

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