(1) Including all who have a right to attend. (2) Complete in all ways.

*Plenary* often shows up in writing referring to the “plenary power” held by a government, and is particularly used for powers mentioned in a constitution. For example, under the U.S. Constitution, the Congress has plenary power to wage war, which means that no one else—not the courts, not the states, not the president—has any power whatsoever to second-guess Congress about warmaking. But in recent years, that hasn't stopped some presidents from starting conflicts that looked a lot like wars to most people. At a conference, the plenary sessions (unlike the various smaller “presentations,” “workshops,” “forums,” and “seminars” that otherwise fill the day) try to bring everyone together in the same room.

(1) Something that fills up or makes perfect; the amount needed to make something complete. (2) A counterpart.

A complement fills out or balances something. We think of salt as the complement of pepper (maybe mostly because of their colors), and the right necktie is a perfect complement to a good suit. *Complement* can also mean “the full quantity, number, or amount” ; thus, a ship's complement of officers and crew is the whole force necessary for full operation. *Complement* is actually most common as a verb; we may say, for example, that a bright blue scarf *complements* a cream-colored outfit beautifully. Don't confuse *complement* with *compliment,* which means an expression of respect or affection.

To reduce in amount by using up.

The *de-* prefix often means “do the opposite of,” so *deplete* means the opposite of “fill.” Thus, for example, a kitchen's food supplies can be rapidly depleted by hungry teenagers. But *deplete* often suggests something more serious. Desertions can deplete an army; layoffs can deplete an office staff; and too much time in bed can rapidly deplete your muscular strength.

Fully or abundantly filled or supplied.

*Replete* implies that something is filled almost to capacity. Autumn landscapes in New England are replete with colorful foliage. Supermarket tabloids are always replete with details of stars' lives, whether real or imaginary. And a professor may complain that most of the papers she received were replete with errors in grammar and punctuation.

(1) Relating to or based on the metric system. (2) Relating to or arranged in meter.

The metric system was invented in France in the years following the French Revolution, and a version of it is now used in most of the world to measure distance, weight, and volume. Basic metric units include the *kilogram* (the basic unit of weight), the *liter* (the basic unit of volume), and of course the *meter* (the basic unit of length—see below). *Metric*—or more often *metrical* —can also refer to the basic underlying rhythm of songs and poetry. So while the scientists' measurements are usually metric, the poets' are usually metrical.

(1) The basic metric unit of length, equal to about 39.37 inches. (2) A systematic rhythm in poetry or music.

*Meter* is a metric measurement slightly longer than a yard; thus, a 100-meter dash might take you a second longer than a 100-yard dash. But the word has a different sense in music, where people aren't separated by whether they use the metric system. For a musician, the meter is the regular background rhythm, expressed by the “time signature” written at the beginning of a piece or section: 2/2, 2/4, 3/8, 4/4, 6/8, etc. Within a meter, you can create rhythms that range from the simple to the complex. So, for example, “America the Beautiful” is in 4/4 meter (or “4/4 time”), but so are most of the rhythmically complex songs written by Paul Simon, Burt Bacharach, or Stevie Wonder. In ordinary conversation, though, most people use “rhythm” to include meter and everything that's built on top of it. In poetry, meter has much the same meaning; however, poetic meters aren't named with numbers but instead with traditional Greek and Latin terms such as *iambic* and *dactylic*.

An instrument used to measure distance traveled.

*Odometer* includes the root from the Greek word *hodos,* meaning “road” or “trip.” An odometer shares space on your dashboard with a speedometer, a tachometer, and maybe a “tripmeter.” The odometer is what crooked car salesmen tamper with when they want to reduce the mileage a car registers as having traveled. One of life's little pleasures is watching the odometer as all the numbers change at the same time.

A device used to measure speed of rotation.

A tachometer is literally a “speed-measurer,” since the Greek root *tach-* means “speed.” This is clear in the names of the *tachyon,* a particle of matter that travels faster than the speed of light (if it actually exists, it's so fast that it's impossible to see with any instrument), and *tachycardia,* a medical condition in which the heart races uncontrollably. Since the speed that an auto tachometer measures is speed of rotation of the crankshaft, the numbers it reports are revolutions per minute, or rpm's.