Greek character that symbolises resistance (5)

I believe the answer is:

omega

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'greek character' is the definition.
(letter from the Greek alphabet)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for omega that I've seen before include "Last (Gk. letter)" , "24th Greek letter" , "letter from abroad" , "End of sequence" , "Consummation" .)

I've seen this clue in The Telegraph.

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