[[Going about asking pharmacists what it means is a noble try but you ought to have consulted a Latin scholar instead. The x is not an x, it is a slash through the stem of the r. As it is pointed out in the article, this is used in other medical abbreviations. It adds nothing to the meaning. It is simply a symbol for abbreviation (like a period at the end of words in Eng.), the abbreviated word being, in all likelihood, recipe, or “take.” Invocation to the gods indeed.]]
I did consult books on abbreviations and medical terminology, and found “rx” and sometimes the others (dx, tx, hx), but no explanations about their origin, or that “x” is commonly used to abbreviate terms. Thanks for that information. From what I have seen, Rx is the only one used as a symbol (with the cross through the leg of the R) and not just an abbreviation like the others. If you look at the Eye of Horus in the website (check the newer version of the Rx mailbag answer now posted - I go from attributing the symbol to Jupiter to giving the Egyptians credit - still invoking gods), you’ll see that the eye symbol also has a leg that hangs down like the bottom of the R. So maybe it evolved from there, and they incorporated the R for “recipe” and crossed the leg to give it the abbreviation “x.” I like that explanation, anyway.