O for the means to disseminate information! (8,6)

I believe the answer is:

circular letter

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'means to disseminate information' is the definition.
(type of letter)

I don't understand how the rest of the clue works.

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(Other definitions for circular letter that I've seen before include "description of second-in-command" , "communication to more than one person!" , "Several people will be sent this" , "One may be copied to several people" .)

I've seen this clue in The Times.

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