What's Plagiarism?

m-w.com gives me the following as a definition for 'plagiarize':

to steal and pass off (the ideas or words of another) as one's own

Pre-theoretically, this sounds right. But I think it might be too limiting. In order to plagiarize, do I *really* have to pass off the work as my own? Allan posted today to Fake Barn Country, starting up the epistemological internalism/externalism debate again. Suppose I posted the following in comments, anonymously.

Suppose we think of virtues in general as excellences of character. A virtue is a stable and successful disposition: an innate ability or an acquired habit, that allows one to reliably achieve some good. An intellectual virtue will then be a cognitive excellence: an innate ability or acquired habit that allows one to reliably achieve some intellectual good, such as truth in a relevant matter. We may now think of justified belief as belief that is appropriately grounded in one's intellectual virtues, and we may think of knowledge as true belief that is so grounded. By adopting this position, we can see the foundationalist's epistemic principles as instances of this more general account of justified belief and knowledge.

I did not author this paragraph -- John Greco did. If I posted it, anonymously, to FBC, without citing Greco or suggesting that I was quoting, I think that I intuitively plagiarize. But it does not seem that I am attempting to pass the work off as my own -- I'm not even identifying myself as the person who posted it. Admittedly, there may be some sense in which I might attempt to pass off the work as 'my own', where I am an anonymous person. I might be hoping that people will think, "the person who posted that comment was very smart". They'd be thinking that about me, even though they don't know that I'm that person. But I can make an even clearer case by supposing that *Allan* anonymously makes that comment on his own post. I've no idea why he'd do such a thing, but it could be done. He, certainly, would not be attempting to pass the comment off as his own. What is the appropriate response? I think we must either deny that this commenting is an act of plagiarism or revise our definition. I don't know how the definition would end up having to look.