As churchgoer, get down to it (5)

I believe the answer is:

crypt

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

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for crypt that I've seen before include "Burial vault" , "Tomb" , "Underground cell" , "Catacomb" , "Church's basement" .)

I've seen this clue in The Guardian.

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