[dyed_in_the_wool]

Thankfully, departments of the government are not the undisputed definers of terms such as that.

True. That's why I first used the Hayek/Friedman definition. According to their Free Market Economics, MicroSoft is a monopoly.
You don't have to like it or believe it, but by restraint of trade, among other things, they are monopolists.
Put another way, ask yourself the last time MicroSoft pushed for an Open Standard for ANYTHING.
We can wait. But I already know what the answer is. In fact, they're justthisverymoment working against the Open XML document consortium that they helped found. Imagine that.
And you wonder why people get pissed having to pay $300 so they can share files with MicroSoft Office users...

[Protagoras]

Put another way, ask yourself the last time MicroSoft pushed for an Open Standard for ANYTHING.

Pushing for open standards doesn't define whether you are a monopolist or not. I know of no companies or individuals who try to help their competitors.

A true monopoly, which is the very rarest of things (absent government, or other force), leaves no options or alternatives. Microsoft doesn't qualify. Not to mention that the main thing that got them in trouble with government regulators (under Bill Clinton's direction) was giving things away for free.