Q. Working on software that has an e-shop, I see a very different use of the word “checkout” vs. “check out.” Should it be “checkout now” or “check out now”?

A. A good dictionary will tell you that it’s “checkout” (one word) as a noun (often used attributively, as in “checkout line”) and “check out” (two words) as a verb. So it should be “check out now.” Or you could save yourself the editorial headaches and use “go to checkout” (or, as Amazon has it, “proceed to checkout”) rather than “check out now.”