One can weaken and still wave it (4)

I believe the answer is:

flag

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'one can' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for flag that I've seen before include "Give a signal" , "Draw attention to" , "Paving stone; iris; tire" , "National emblem; tire" , "Iris - paving slab" .)

I've seen this clue in the Evening Standard.

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