What one gets, having sex in Welsh party (not quietly) (4)

I believe the answer is:

laid

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'what one gets having sex in welsh' is the definition.
I can't judge whether this defines the answer.

'party not quietly' is the wordplay.
'party' becomes 'l'.
'not quietly' becomes 'aid' (I can't explain this - if you can you should believe this answer much more).
'l'+'aid'='LAID'

Can you help me to learn more?

(Other definitions for laid that I've seen before include "settled" , "Produced eggs" , "(Of dining table) set" , "Flattened by wind and rain" , "Deposited" .)

I've seen this clue in The Independent.

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