A person who or thing which communicates (something) (in various senses).

A person who holds communication with another, esp. secret communication; a confederate, accomplice. Obsolete.

A means by which communication (of information, etc.) is effected; (in later use esp.) a substance used for communication.

An agent or means of intercommunication.

A user of language; a communicator.

an intermediary in a transaction; a go-between; one who carries or supplies information (cf. sense 2d above).