Crossword Genius

Advised to be in underwear? (7)

Ross

I believe the answer is:

briefed

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

'advised' is the definition.
The definition and answer can be both to do with communicating as well as being past participle verbs.
Perhaps they are linked in a way I don't understand?

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for briefed that I've seen before include "Prepared" , "Instructed in advance" , "Informed of the facts" , "Advised or instructed, like barrister" .)

I've seen this clue in The Guardian.
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