The study of the occult significance of numbers.

As an element of astrology and fortune-telling, numerology has long been employed to predict future events. For many early Christians, 3 represented the Trinity, 6 represented earthly perfection, and 7 represented heavenly perfection; and still today, many of us like to group things into sets of 3 or 7, for no particular reason. Numerology has also been used to interpret personality; in particular, *numerologists* may assign numbers to each letter of a person's name and use the resulting figures, along with the person's date of birth, as a guide to his or her character.

Having or using both letters and numbers.

Alphanumeric passwords are much harder for a hacker to crack than plain alphabetic passwords, since the number of possible combinations is so much greater. License plates usually contain both letters and numbers, since, for a big state or country, the plate wouldn't be large enough to fit enough numbers for everyone. In computing, the standard alphanumeric codes, such as ASCII, may contain not only ordinary letters and numerals but also punctuation marks and math symbols.

To specify one after another; list.

In a census year, the U.S. government attempts to enumerate every single citizen of the country—a task that, even in the modern era of technology, isn't truly possible. Medical tests often require the *enumeration* of bacteria, viruses, or other organisms to determine the progress of a disease or the effectiveness of a medication. Despite its *numer-* root, you don't have to use numbers when enumerating. For students of government and law, the “enumerated powers” are the specific responsibilities of the Congress, as listed in the U.S. Constitution; these are the only powers that Congress has, a fact that the Tenth Amendment makes even more clearly.

Exceeding the usual number.

*Supernumerary* starts off with the Latin prefix *super-*, “above” (see SUPER). You may have heard of someone being born with supernumerary teeth, supernumerary fingers, or supernumerary toes. A supernumerary rainbow may show up as a faint line—red, green, or purple—just touching the main colored arc. *Supernumerary* is also a noun: A supernumerary is usually someone in a crowd scene onstage, otherwise known as an “extra” or a “spear-carrier.”

A unit of computer information equal to 1,024 bytes.

Knowing the root *kilo-*, you might think a kilobyte would be exactly 1,000 bytes. But actually a kilobyte represents the power of 2 that comes closest to 1,000: that is, 210 (2 to the 10th power), or 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2, or 1,024. Why 2? Because the capacity of memory chips is always based on powers of 2. Locations in electronic memory circuits are identified by binary numbers (numbers that use only the digits 0 and 1), so the number of addressable locations becomes a power of 2.

A unit of length equal to 1,000 meters.

A kilometer is equal to about 62/100 of a mile, and a mile is equal to about 1.61 kilometers. The U.S. has been slow to adopt metric measures, which are used almost everywhere else in the world. Though our car speedometers are often marked in both miles and kilometers, the U.S. and Great Britain are practically the only developed nations that still show miles rather than kilometers on their road signs. But even in the U.S., footraces are usually measured in meters or kilometers, like the Olympic races. Runners normally abbreviate *kilometer* to *K*: “a 5K race” (3.1 miles), “the 10K run” (6.2 miles), and so on.

A unit of frequency equal to 1,000 cycles per second.

If your favorite AM radio station has a frequency of 680 kilohertz (kHz), that means the station's transmitter is oscillating (vibrating) at a rate of 680,000 cycles per second (i.e., 680,000 times a second). A related term is *megahertz* (MHz), meaning “*millions* of cycles per second.” Shortwave radio operates between 5.9 and 26.1 MHz, and the FM radio band operates between 88 and 108 MHz. Garage-door openers work at about 40 MHz, baby monitors work at 49 MHz, and so on. The terms *hertz, kilohertz* and *megahertz* honor the great German physicist Heinrich Hertz, the first person to broadcast and receive radio waves.

A unit of weight equal to 1,000 grams.

The original concept of the kilogram, as the mass of a cubic decimeter of water (a bit more than a quart), was adopted as the base unit of mass by the new revolutionary government of France in 1793. In 1875, in the Treaty of the Meter, 17 countries, including the U.S., adopted the French kilogram as an international standard. In 1889 a new international standard for the kilogram, a metal bar made of platinum iridium, was agreed to; President Benjamin Harrison officially received the 1-kilogram cylinder for the U.S. in 1890. But no one uses that bar very often; for all practical purposes, a kilogram equals 2.2 pounds.