onion

onion plant of the family Liliaceae ( lily family), of the same genus ( Allium ) as the chive ( A. schoenoprasum ), garlic ( A. sativum ), leek ( A. porrum ), and shallot ( A. ascalonium ). These plants are characterized by an edible bulb composed of food-storage leaves that are rich in sugar and a pungent oil, the source of its strong taste. The above-ground green leaves, typically long and tubular, are also eaten. All these species are believed to be native to SW Asia and are known to have been cultivated since ancient times. The onion ( A. cepa ), no longer found wild, is a biennial now grown in many varieties throughout the world as a table vegetable. Common varieties include the strong-flavored red onion, the milder yellow onion, and the bland white onion. Pearl onions are small white onions used for pickling. The large Spanish and Bermuda onions have a delicate flavor. The onion was grown extensively by the ancient Egyptians, in whose writings it is mentioned, and was later spread by the Spanish colonists. The more pungent garlic, a perennial, has a bulb consisting of small bulbils called cloves. This part is most often used in cooking, chiefly as flavoring; garlic is especially popular in the Mediterranean region and East Asia. Used as a folk remedy for thousands of years, scientific investigation is confirming garlic's usefulness as a blood thinner, antioxidant, and cancer preventive. The shallot (supposedly introduced to Europe from Ascalon, or Ashqelon, by the Crusaders, hence the botanical name) is a perennial with clusters of small onionlike bulbs. It and the more familiar leek, a biennial with a small single bulb, are both commonly used fresh in salads, as asparaguslike cooked vegetables, and in soups and stews. The leek, cultivated in ancient Egypt and probably introduced to England by the Romans, is the floral emblem of the Welsh, who adorn their hats with its leaves on St. David's Day. Scallion is a popular term for any edible Allium with a reduced bulb, especially the leek and shallot. The Welsh onion ( A. fistulosum ) is a leeklike plant popular in Asia. The chive, today found wild in Italy and Greece, is a hardy perennial sometimes used as an ornamental border plant. For flavoring, its leaves are the most desirable portion. Several species of Allium are native to North America, chiefly in the West, where the edible types were collected by Native Americans. Because of the disagreeable odor and taste imparted to the milk of cows that feed upon them, some species are considered weeds, especially the common wild garlic, A. vineale, naturalized from Europe. Onion is classified in the division Magnoliophyta , class Liliopsida, order Liliales, family Liliaceae.

onion know one's onions be very knowledgeable about something.
not the only onion in the stew not the only person or thing to be considered.
onion dome a dome which bulges in the middle and rises to a point, used especially in Russian church architecture.