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annual rings

(Encyclopedia)annual rings, the growth layers of wood that are produced each year in the stems and roots of trees and shrubs. In climates with well-marked alternations of seasons (either cold and warm or wet and dr...

nitrous oxide

(Encyclopedia)nitrous oxide or nitrogen (I) oxide, chemical compound, N2O, a colorless gas with a sweetish taste and odor. Its density is 1.977 grams per liter at STP. It is soluble in water, alcohol, ether, and ot...

avocet

(Encyclopedia)avocet ăvˈəsĕt [key], common name for a long-legged wading bird about 15 to 18 in. (37.5–45 cm) long, related to the snipe and belonging to the same family as the stilt. The American avocet or b...

parcel post

(Encyclopedia)parcel post, sending of packages through the mail service. At the congress of the Universal Postal Union in Paris in 1878, an international parcel-post system was established. The British parcel-post ...

yarrow

(Encyclopedia)yarrow, a plant of the genus Achillea, perennial herbs of the family Asteraceae (aster family), native to north temperate regions. Several species are cultivated as ornamentals for their flat-topped c...

blenny

(Encyclopedia)blenny, common name of various species of extremely numerous small fishes belonging to the suborders Blennioidei (blennies) and Notothenioidei (Antarctic blennies). They are characterized by elongated...

Tagus

(Encyclopedia)Tagus tāˈgəs [key], Span. Tajo, Port. Tejo, river, c.585 mi (940 km) long, rising in the mountains E of Madrid, E Spain, and draining the central part of the Iberian Peninsula. The Tagus flows nort...

thresher shark

(Encyclopedia)thresher shark, long-tailed, warm-water shark, genus Alopias. The upper fork of its tail is slender and sickle-shaped and is about equal in length to the rest of the body. This shark uses its tail str...

sodium hydroxide

(Encyclopedia)sodium hydroxide, chemical compound, NaOH, a white crystalline substance that readily absorbs carbon dioxide and moisture from the air. It is very soluble in water, alcohol, and glycerin. It is a caus...

sodium silicate

(Encyclopedia)sodium silicate, any one of several compounds containing sodium oxide, Na2O, and silica, Si2O, or a mixture of sodium silicates. Sodium orthosilicate is Na4SiO4 (or 2Na2O·SiO2); sodium metasilicate i...