The word “atonement” looks for all the world like a Greek or Latin theological term, but it really is pure English. It is derived from the Middle English verb atonen, “to become reconciled,” which in turn comes from the prepositional phrase at on, lit. “at one” or “in harmony.” Therefore, dividing the word up as at-one-ment is not as ridiculous as it looks and really is instructive. To get the sense of the word, consider Tyndale’s rendering of 2 Cor. 5:20: “We pray you in Christes stede that ye be atone with God” (KJV says “reconciled”).
The word “atonement” appears 69 times in the KJV OT (and only once in the KJV NT!) Most commonly this is a rendering of the Hebrew verb kaphar “to cover,” which is usually translated something like “to make an atonement.” The noun appears as a plural, kippurim (lit. “atonements”). In Modern Hebrew, the archaic plural has been replaced by a singular, such as we see in the expression Yom Kippur, the Day of Atonement.
How do we get from “cover” to “atonement”? To “cover” sin has the unfortunate connotation in English of “hiding” sin, or perhaps of repenting in only a superficial way (cf. the expression “a cover-up”). Consider 1 Pet. 4:8: “And above all things have fervent charity among yourselves: for charity shall cover the multitude of sins.” The JST changes “shall cover” to “preventeth,” so as to keep the passage from being misconstrued in English. Something like the JST is probably necessary to keep the passage from being misconstrued in English; cf. the NEB: “because love cancels innumerable sins.” But if we understand the Semitic origin of the expression there should be no misunderstanding. You can kind of see the sense in English by thinking of the expression “to cover a bet,” which does not mean to hide anything.
Nibley, in his Ensign series on “The Atonement of Jesus Christ” (see July, August, September and October 1990 Ensigns for this four-part series) connected this conception of atonement to ritual embraces. From the basic sense of covering or encircling with the arms comes the Arabic kafata or suppliant embrace, which he sees as underlying 2 Nephi 4:33: “O Lord, wilt thou encircle me around in the robe of thy rightesousness!” For visual representations of such embraces, he points to the ritual embrace (hpt) of the Egyptian funerary texts (for illustrations, see here). And, of course, although Nibley doesn’t explicitly make the connection, he certainly intends for us to extend the concept to our own ritual form of embrace, which we experience in the temple.
Such an embrace represents a return to the presence of our Father, a reunion, where we may be reconciled to him and once again be “at one” with him.