Zed: The British word for Z, the only letter Shakespeare ever used as an insult: “Thou whoreson zed, thou unnecessary letter!” (King Lear II, ii)
Zeugma: a pun employing the same word with two different meanings in one sentence: “The patient wasn’t.”
zero: One less than one, from the Arabic sifr, “cipher.” The addition of zero to the set of whole numbers facilitated momentous mathematical achievements in the Arabic world, achievements not possible among Westerners hampered by the inflexible numerical system of the Romans and Greeks. (Aristotle offered as proof of the unique intelligence of mankind, the fact that some people could be taught long division.) As the indisputable practicality of Arabic numerals overcame the prejudice of religious zealotry, a number of Arabic words made their way into Western Europe: algebra, azimuth, zenith.
