Just a hint in a letter from abroad (4)

I believe the answer is:

iota

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'letter from abroad' is the definition.
(letter of the Greek alphabet)

I don't understand the remainder of the clue.

(Other definitions for iota that I've seen before include "little part" , "Greek letter of little value" , "Ninthe letter of the Greek alphabet" , "Smidgen" , "Greek letter - small quantity" .)

I've seen this clue in The Globe and Mail.

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