The state of being a mother; motherhood.

*Maternity* is used as both a noun and an adjective. *Maternity benefits* are benefits specially provided by employers for women having babies, and usually include *maternity leave,* time off work. With maternity come *maternal* feelings, which are shown by all species of warm-blooded animals as well as a few reptiles such as crocodiles and alligators.

A woman who controls a family, group, or government.

A *matriarchy* is a social unit governed by a woman or group of women. It isn't certain that a true *matriarchal* society has ever existed, so matriarchy is usually treated as an imaginative concept. But there are societies in which relatedness through women rather than men is stressed, and elements of matriarchy may be stronger in certain societies than they are in most of the Western world. And most of us can point to families in which a woman has become the dominant figure, or grande dame, or matriarch.

Based on or tracing the family through the mother.

A person's *lineage* is his or her *line* of ancestors. So *matrilineal* means basically “through the mother's line,” just as *patrilineal* means “through the father's line.” *Matrilineality* is an important concept in anthropology; among other things, it usually determines who will inherit property on a person's death. Though families that follow the European model take the father's name and are therefore patrilineal, matrilineal societies have existed around the world, including among various American Indian tribes.

(1) Something (such as a situation or a set of conditions) in which something else develops or forms. (2) Something shaped like a pattern of lines and spaces.

In ancient Rome, a *matrix* was a female animal kept for breeding, or a plant (sometimes called a “parent plant” or “mother plant”) whose seeds were used for producing other plants. In English the word has taken on many related meanings. Mathematicians use it for a rectangular organization of numbers or symbols that can be used to make various calculations; geologists use it for the soil or rock in which a fossil is discovered, like a baby in the womb. And *matrix* was a good choice as the name of the reality in which all humans find themselves living in a famous series of science-fiction films.

The farming of plants and animals (such as kelp, fish, and shellfish) that live in the water.

For most of the modern history of aquaculture, only costly fish and shellfish like salmon and shrimp were harvested. But new technologies are allowing cheaper and more efficient cultivation of fish for food, and such common fish as cod are now being farmed. Seaweeds and other algae are also being grown —for food (mostly in Asia), cattle feed, fertilizer, and experimentally as a source of energy. Aquaculture is now the world's fastest-growing form of food production.

A scuba diver who lives and works both inside and outside an underwater shelter for an extended time.

*Aquanaut* combines *aqua* with the Greek *nautes*, meaning “sailor.” Like *astronaut* and *aeronaut*, the word may remind you of those mythical Greek heroes known as the Argonauts, who sailed with Jason on his ship, the *Argo*, in quest of the Golden Fleece. Various underwater habitats for aquanauts, such as Conshelf, SEALAB, and MarineLab, have captured the public imagination since the 1960s.

(1) A pipe or channel for water. (2) A bridgelike structure for carrying water over a valley.

Based party on the Latin *ducere*, meaning “lead” or “conduct” (see DUC/DUCT), the word *aqueduct* named an ancient civil-engineering marvel. You may have seen photos of the great arches of ancient aqueducts spanning valleys in countries throughout the old Roman Empire, practical pipelines that are also regarded as works of timeless beauty. From the 20th century, the 242-mile Colorado River Aqueduct, the 336-mile Central Arizona Project, and the 444-mile California Aqueduct are considered wonders of American engineering, but they are not renowned for their beauty. Most aqueducts today either are riverlike channels or run underground, perhaps appearing simply as a long mound.

A layer of rock, sand, or gravel that can absorb and hold water.

The vast but relatively shallow Ogallala Aquifer lies beneath the Great Plains, under portions of eight states. Its thickness ranges from a few feet to more than a thousand feet. The Ogallala yields about 30 percent of the nation's groundwater used for irrigation in agriculture, and provides drinking water for most of the people within the area. But for many years more water has been extracted from the Ogallala than has been returned, and the situation today is of great concern.