Advocates underwear (6)

I believe the answer is:
briefs
This could be a double definition.
'advocates' is the first definition.
The answer and definition can be both to do with communicating as well as being verbs in their -s form.
Maybe there's a link between them I don't understand?
'underwear' is the second definition.
(I've seen this before)
Can you help me to learn more?
(Other definitions for briefs that I've seen before include "Case summaries drawn up for barristers" , "Sets of instructions for lawyers" , "They are prepared for barristers' perusal" , "Underpants, knickers" , "by which privates will be constrained" .)
