Japan? Go around mid-April (7)

I believe the answer is:

varnish

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'japan?' is the definition.
(I've seen this before)

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

(Other definitions for varnish that I've seen before include "Glossy stain" , "Glossy coat" , "Protective coating" , "Wood or nail coating" , "Shiny transparent coating used on wood" .)

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

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