“Demo, drop-down, drop down list”, “how can I make this? “, is my philosophy” in knowledge-management? Another thread dealt with this nicely. The link specifies grammatically this could be considered a compound adjective, so the hyphen is acceptable. Undoubtedly the word “dropdown” appears more often in searching (According to Google ) when comapared with a slightly more obscure term like “combobox”. Is it because a term “dropdown” is generic? This may change with trends change, but for now, “dropdown” or “drop-down” seems more widely searched. If your document is meant for internal use then you should use whichever word your readers or users may know best.