Crossword Genius

Gave letters of authorisation to (10)

Ross

I believe the answer is:

initialled

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'gave' 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 don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for initialled that I've seen before include "Indicated approving" , "two or three nominal reductions?" , "Recorded agreement" .)

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