Some power painter has to dismiss Monet’s water (4)

I believe the answer is:

watt

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'some power' is the definition.
(I've seen this before)

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

(Other definitions for watt that I've seen before include "Unit of power -- Scottish engineer, d. 1819" , "Unit of power - Scottish inventor" , "Worker in steam" , "James - - (Scottish inventor)" , "man of power?" .)

I've seen this clue in The Times.

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