Mythical giant eyed quite remarkably (5)

I believe the answer is:

argus

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'mythical giant' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for argus that I've seen before include "Alert watchman" , "Small butterfly" , "Type of butterfly" , "Monster with many eyes slain by Hermes in Greek myth" , "Giant with one hundred eyes in Greek mythology" .)

I've seen this clue in the Evening Standard.

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