Private trials, maybe (6-7)

I believe the answer is:

courts-martial

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

'private' is the definition.
Both the answer and definition are adjectives.
Maybe they are linked in a way I don't understand?

I can't explain the rest of the clue.

Can you help me to learn more?

I've seen this clue in The Irish News.

Want a hint initially instead of a full solution? Install my app