The words we'll use for Word-a-Day come from this list of English words local elementary school students & senior high school students must learn before graduating. Underlined ones are the Elementary level.
--- do (does, did, done), have (has, had), can (could), will (would), may (might)
---must, shall, should
---about, above,across, after, against, along, among, around, at, before, behind, below, beside, between, beyond, by, down, during, except, for, from, in, in back of, in front of, inside, into, like, near, of, off, on, out, out of, outside, over, next to, since, than, through, till, to, toward, under, until, up, upon, upper, with, without