Crossword Genius

A thin layer of material surrounded astronaut's home by the second day of the week (6)

Ross

I believe the answer is:

tissue

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'week' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for tissue that I've seen before include "Bodily matter" , "light material" , "See 17" , "Thin soft disposable paper" , "Thin fabric" .)

I've seen this clue in The Irish Times.
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