Initial letter (5)

I believe the answer is:

alpha

This clue is a double definition.

'initial' is the first definition.
(thesaurus)

'letter' is the second definition.
(NATO phonetic alphabet)

(Other definitions for alpha that I've seen before include "Foreign character" , "Burrowing American rodent" , "letter opener" , "leader in Athens, originally" , "First letter of the Greek alphabet" .)

I've seen this clue in the Evening Standard.

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