Shred a letter to Aristotle Onassis (4)

I believe the answer is:

iota

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'aristotle onassis' is the definition.
The definition suggests a singular noun which matches the answer.

'shred a letter to' is the wordplay.
'shred' is an anagram indicator (I've seen 'shredded' mean this).
'letter' becomes 'i'.
'a'+'i'+'to'='aito'
'aito' is an anagram of 'IOTA'.

Can you help me to learn more?

(Other definitions for iota that I've seen before include "Trace" , "Greek letter - minimal amount" , "Old letter" , "Greek letter of little value" , "Ninth Greek character" .)

I've seen this clue in The Times.

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