I think you should be able to reuse an assignment if you wrote it

In the Webster definition of plagiarism, recycling one's own papers would fall under "to present as new and original an idea or product derived from an existing source" and is, therefore, considered plagiarism. What do you think? 

What if you wrote it, but it was never graded or you withdrew from the course and now want to use the same paper again for the same course?  Does that make a difference?  I am interested in hearing your thoughts!  Do a little research to see if you can find any opinions supporting one view or another (especially any that might consider it ethical and/or not plagiarism).