Depending on your thinking, Google's new Chromecast TV device either is, or isn't a dongle. "What's a dongle," you say? Aha...that, dear reader, is the right question.
Chromecast is a little bit of hardware, approximately the size and shape of a pack of chewing gum. At one end is a metallic connector that's meant to stick into a bigger piece of hardware--in this case a TV set, via an HDMI port--and without being connected to said bigger hardware, the smaller piece of hardware won't do anything.
A dongle you see, has a much older technical meaning. Webopedia.com offers a succinct definition of the meaning of this geeky word:
A device that attaches to a computer to control access to a particular application. Dongles provide the most effective means of copy protection. Typically, the dongle attaches to a PC's parallel port. On Macintoshes, the dongle sometimes attaches to the ADB port. The dongle passes through all data coming through the port so it does not prevent the port from being used for other purposes. In fact, it's possible to attach several dongles to the same port.
This is the thing that the Chromecast-isn't-a-dongle folks are talking about. I remember using one years ago in school--you couldn't access the CAD package loaded on the computer unless there was a dongle stuck in the right socket. These physical DRM devices were fairly common, in an era where pirating software on a floppy disk was relatively easy and there wasn't necessarily a Net connection available so that the software could dial home and confirm it was a genuine copy.
But Wikipedia offers a slightly different definition:
A hardware key (commonly known as a dongle) is an electronic copy protection and content protection device which, when attached to a computer or other electronic appliance, unlocks software functionality or decodes content. The hardware key is programmed with a product key or other cryptographic protection mechanism; it attaches via electrical connector to an external bus of the computer or appliance.
That "decodes content" thing is key. Wikipedia's entry even states, "When used as a device attached to a computer or TV or gaming console, dongles can enable functions that would not be present without" them. Google's Chromecast dongle basically decodes the special wireless signals being sent to it from a compatible device, such as an Android phone, and sends ongoing signals to the TV hardware, to add services the TV would otherwise be without. Which means that Chromecast is a dongle.
The meaning of words, you see, evolves. We all call our various iPhones, Galaxies, and whatnots, for example, "phones." As in telephone. And that is often the very last thing we use our smartphones for nowadays.
Chromecast is a dongle. Let the donglewars begin!