Just a quick note to agree with Mikkel and Aleks, and add a detail about how we use these words. As you read, "media" is plural, and "medium" is singular.
When we talk about news sources, we rarely will refer to a single news source as a "medium." We think of news sources collectively (as a group), so usually we refer to "media" or "the media."
"Medium" has many meanings, but the one most closely connected to "media" is (loosely translated) "substance of transmission/movement," or "environment, condition." It is most often used in technical contexts, so it is not used in everyday, informal communication. For example:
"Water is the medium through which fish swim."
"Viruses can pass through the medium of the cell membrane (cell wall)."
"We see through the medium of our eyes."