Clothing becomes a zombie? (6)

I believe the answer is:

undies

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'clothing' is the definition.
(undies is a kind of clothing)

I cannot understand how the remainder of the clue works.

(Other definitions for undies that I've seen before include "clothing not normally seen" , "Pants" , "linen" , "Undergarments (colloq.)" , "Knickers (abbrev.)" .)

I've seen this clue in The Sun and The Telegraph.

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