A site visitor asked about the correct usage of a word used to describe meetings held in a face-to-face format rather than in a classroom-seating orientation. Is such a gathering a round table, or a roundtable?
When describing a piece of furniture with a circular surface, we write “round table.” But as often occurs when a quotidian term develops a new sense, the treatment changes. Unfortunately, this development is haphazard and inconsistent, partly because we are within the transition zone for much of our vocabulary, and various dictionaries may diverge in their treatment of a specific term. However, the predominant form for the sense of “face-to-face group meeting” is now roundtable. (But maintain distinctions for various senses: “King Arthur’s Round Table was literally a round table as well as an assembly of his supporters, at which they not only feasted but also held roundtables.”)
This type of evolution occurs often in commercial and organizational contexts. Other open compounds undergoing such a transformation include “life cycle” (to describe the cyclical nature of products and systems) and “road map” (in reference to the course an organization takes for itself or for a product or service). However, in the biological sense of “life cycle” and the literal cartographic sense of “road map,” these compounds remain open, though that status may change. (See this post, which describes the life cycle of compound words.)
Why does this change occur? Humans have a natural tendency to simplify or consolidate things, including language. And in an open system such as language development, it is easy for nonstandard terminology (slang, jargon, and so on) and treatment (abbreviation, contraction, capitalization, spelling, and so on) to take hold and prevail. When writers make assumptions without verification about how compound words are styled—including such transitional forms as by-product and mind-set, styling them byproduct and mindset—those forms replicate virally as others see them in published materials and uncritically employ them.
That is the process of evolution by which “round table” will almost inevitably become roundtable not just in organizational jargon but also in everyday use to describe household furniture, and by which lifecycle and roadmap are likely to someday apply in all connotations, and by which byproduct and mindset will become standard. But the tipping point for these forms has not yet arrived, so continue to refer to reputable sources and observe the “round table”/roundtable distinction as well as the others noted here.