"Artifact" Is Not in the Dictionary (Though "Gullible" Is):

Not in the Oxford English Dictionary, that is to say. I was quite surprised to see that; the reason, I take it, is that the British spelling is "artefact," but my sense is that the OED is usually quite good at including the American spellings, and a quick search through British newspapers shows that even they use "artifact" on occasion. Let this be a reminder that even the most reputable sources have glitches; better to check two sources rather than relying on any one.