Galvanise more than half of Spanish gypsies (4)

I believe the answer is:

zinc

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

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

(Other definitions for zinc that I've seen before include "Blue-white metal" , "Antioxidant element" , "Bluish-white metal" , "Metal much used in alloys" , "trace element" .)

I've seen this clue in The Sunday Times and The Times.

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