Submit here for publishing consideration and community feedback. It depends who you talk to.
Some sources maintain that both are correct.
Others prefer the single word. The single word for both noun and verb seems to be the most common usage, so that s the one we will be using throughout. That example should give you a little insight into the issues the copyeditor deals with on a daily basis, though. She s probably an incredibly detail-oriented, patient, and underpaid word and fact lover with a library filled with reference books, and an unerring instinct. It s an instinct for when to look things up, and where to go for the right information .