I've always thought that "author" was British and "writer" was American, but still has the same meaning. Might be wrong, though.
... and having a non-fiction essay published in a non-paying but highly respected academic journal might require further definition on a CV/Resume
If the definition is that someone else has paid you for your work, then if you've self-published on Amazon, for example, and other people have bought your work, it would appear to qualify.
It is interesting to follow the discussions in this thread. I have sold short stories to traditional, paying markets. I suppose that qualifies me to say I'm a 'published author,' although I never use that term. I have a self-published book I wrote for my daughter and put on Amazon. It has made just over $1000 since I published it. For many, that does not, in and of itself, qualify me to say I'm a published author. I've had a couple of agents interested in the book, and if I were ever to pursue that interest with them, and if the book were to be traditionally published, then suddenly I'm a published author before the traditional publisher sells even one copy. Something doesn't make sense there. If it comes down to being paid, then for my children's book alone I've been paid more than someone publishing in a prestigious literary journal for contributors copies. What about self-published authors who are out-selling traditionally-published mid-list authors? Yes, they exist. They're not published authors, but the poorer performing mid-list authors are? The unifying theme seems to be that it doesn't matter whether you're being paid, it matters who is paying you. It has to be an editor and not just the unwashed masses (never mind the fact that the traditional editor is relying on those same unwashed masses, ultimately, for sales and to send you a royalty check). I have to concur with the statements above that it is more a sort of elitism than any rational distinction that has to do with whether one is being paid for one's writing. You have to go through the proper ritual of submission, rejection, submission, ultimate acceptance, and so on. Your work is blessed by an appropriate editor somewhere and then you're initiated into the hallowed ranks of published author. The problem is, that distinction no longer makes sense in the current publishing landscape in terms of being a 'published author.' At least, it makes no sense when you're trying to use an economic justification of being paid for one's writing. It only makes sense if you're using more of an elitist, "old boys club" approach to the issue.
@Steerpike, there is always going to be a stigma against self-published books. However, when writing "Published Writer" or something similar on a CV, I think there are some professional considerations that need to be taken into account. If a person in the publishing business was evaluating your CV and saw that you've listed yourself as a published writer, he might take it as a sign of dishonesty to see a list of self-published books. Perhaps in such cases it is better to be clear and write "Self-published Writer" instead.
I still don't understand in what context one would put "published writer" on a C.V./resume in and of itself. If part of a C.V., any relevant publications are listed under a heading of published works. Those works would indicate the publisher, date of publication, etc. Self-published works would be self evident. There would be no place to put "published writer." If one is putting "writer" as a job on a resume, I would still think that underneath that heading, one would list what was published. (Or, if there are many, one could write something like, "My work has appeared in numerous periodicals, including The New Yorker, Glimmer Train, Science Fiction Review, and Dog Fancy." ) If you're pitching a novel to an agent, then you'd put information about what you've published in your cover letter -- you wouldn't typically include a resume. If you're using a resume for a job that is totally unrelated to writing wouldn't matter. You could, of course put writing in hobbies, and that is the only place I could think of where you'd put "published writer," but in that case it wouldn't matter much in either case.
