Crossword Genius

A judicial procedure in court (6)

Ross

I believe the answer is:

atrial

I'm a little stuck... Click here to teach me more about this clue!

'in court' is the definition.
(I've seen this before)

'a judicial procedure' is the wordplay.
I cannot quite understand how this works, but
'a' is present in the answer.
The remaining letters 'trial' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for atrial that I've seen before include "referring to Chambers?" , "Like some courts" , "of the heart cavities" , "Like main court" , "Lariat (anag)" .)

I've seen this clue in The Guardian.
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